JP2011141925A - Offset correction value measuring method of magnetic disk device, offset correction method, and magnetic disk device to which the method is applied - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an offset correction value measuring method in a magnetic disk medium of high TPI (Track Per Inch) and a magnetic disk medium of DTM (Discrete Track Medium)/BPM (Bit Patterned Medium). <P>SOLUTION: The offset correction value measuring method includes stages of: writing temporary offset measuring data by a write core while performing on-track control of each positional information area; setting a temporary offset correction value by detecting a position in a radial direction where the output level of the temporary offset measuring data read from tracks by a read core becomes the maximum; learning PRO correction information while the read core is positioned in a track center to perform PRO tracking control about a track of a measuring object; and offsetting the read core by the temporary offset correction value from the track of the measuring object and calculating an offset correction value in which a RPO positional error value becomes zero in the state where the write core is corrected by the temporary offset correction value while making RPO control by the learned RPO correction information. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a disk-shaped recording medium, particularly a magnetic disk on which a magnetic medium in which position information is formed in advance on a magnetic medium such as DTM (discrete track medium) or BPM (bit patterned medium). The present invention relates to an offset correction value measurement method, an offset correction method, and a magnetic disk device to which the method is applied, which are suitable for a magnetic disk device equipped with a magnetic disk medium having a high track density (high TPI).

  Uniform position information is recorded on a magnetic recording medium in a storage device using a conventional general disk-shaped recording medium, for example, a disk drive device such as an HDD (hard disk drive). Position control is performed as a reference. Furthermore, in the present general recording / reproducing magnetic head, the formation positions of the read core (read head / read head) and the write core (write head / write head) in the slider are different. Therefore, when positioning with the rotary positioner, the relative radial position of the read core and the write core with respect to the disk-shaped recording medium differs when positioned at any position of the rotational radius. Since the positioning information can be read only by the read core, the position information read by the read core differs between when the read core is positioned at the target track position and when the write core is positioned. Even in such a case, it is necessary to be able to accurately control the position, particularly with respect to the light core. Here, the accurate position control means that the trajectory through which the read core passes and the trajectory through which the write core passes are in a certain condition, for example, the written data can be read accurately and even if the data is written to the tracks on both sides, This indicates that the data is not erased, and that the control is performed so that the trajectory is almost the same in a situation where the data is not erased. As long as the above condition is satisfied, the trajectory through which the read core passes and the trajectory through which the write core passes may not completely overlap. Of course, it is needless to say that all the available tracks existing on the disk-shaped recording medium need to be established. Note that the offset correction means correcting the relative radial position of the read core and the write core with respect to the disk-shaped recording medium described above, and correcting so that both head cores pass the same track orbit. .

  Conventionally, as an accurate offset correction method for the read core and the write core, only a method having one offset correction value for each track or a method having only one offset correction value for a plurality of tracks is known. Since this conventional method needs to be performed by another method for correcting the position information of the servo sector unit, which is the smallest unit on the track, usually, eccentric correction, RRO (Repeatable Run Out) correction, In the case where the eccentricity is low and the same eccentricity in continuous tracks, the correction target, ZAP (zero acceleration path) control, mainly high-order eccentricity, A case where the phase and amplitude are different is used in the case of a correction target or the like (Patent Documents 2 to 4). However, the conventional correction method is based on the premise that the position information formed on the concentric circles has a similar shape close to a perfect circle. In a disk-shaped recording medium, further increase in track density in the future (higher track density (TPI / track per inch)), or position information on the magnetic medium in advance such as DTM / BPM may be formed. If implemented, it is assumed that the similar shape close to the perfect circle of the track to be corrected collapses locally or entirely, so a situation exceeding the allowable range that can be corrected by the conventional correction method is assumed. . That is, the allowable range of the condition described in the paragraph <0002> is exceeded, the tracks of the read core and the write core do not overlap, and there is a possibility that the track data cannot be read accurately.

  On the other hand, in a disk drive device using a disk-shaped recording medium such as a hard disk drive device, it is required to increase the track density of the disk-shaped recording medium for the purpose of improving the recording density. As the track density increases, higher precision in position control is required. However, in a disk drive device using a disk-shaped recording medium, a certain amount of error or fluctuation is always caused by the physical limitations of the device. The problem of eccentricity, which occurs in the form of eccentricity and becomes larger as the required accuracy increases, becomes more serious. This eccentricity occurs at the time of STW (servo track write) performed before shipment of the disk drive device or at the time of formation of the embedded servo signal formed in the manufacturing process such as DTM / BPM, and the disk-shaped recording medium to the disk drive device. Means a trajectory deviating from an ideal trajectory (perfect circle), such as a disc axis deviation of the disc-shaped recording medium when the disk is mounted, and the amount of eccentricity, that is, the magnitude, is the manufacture of a disc drive device using the disc-shaped recording medium In most cases, it is automatically determined to some extent from the method and the physical dimensions of the disk drive using the disk-shaped recording medium. As described above, since the magnitude of the eccentricity (RRO) is determined by physical constraints, even if the track density becomes high, the magnitude is not reduced in a proportional manner. That is, the absolute value of the eccentricity (RRO) hardly changes even at a high track density.

  In order to make this eccentricity apparently small, for example, the following processing is performed at the initial stage of the test process before shipment of the disk drive device. First, DFT (Discrete Fourier Transform) is performed by a DSP (Digital Signal Processor) of a disk drive device on position information obtained by servo demodulation on a predetermined specific track (data area) of a disk-shaped recording medium. ) Etc. to obtain the necessary eccentricity correction amount. This eccentricity correction amount is stored as an eccentricity correction table on the DSP memory, and this eccentricity correction table is further stored in a flash ROM or the like. When the disk drive device is started next time, the eccentricity correction table is read from the flash ROM or the like, transferred to the DSP memory, and the DSP performs eccentricity correction control based on the eccentricity correction table. As a result, for each recording / reproducing magnetic head, stable on-track operation was enabled through all the cylinders. This eccentricity correction control is called RRO follow-up control, and the meaning of follow-up here means that the RRO is always learned and the latest RRO is followed. Further, the eccentricity correction control that always operates with the fixed RRO correction information without learning the RRO correction information is called RRO control, and is defined separately from the RRO tracking control.

  Such a track eccentricity of the disk-shaped recording medium includes many order components (frequency components) due to various factors. Among these, low-order eccentricity such as the primary component and the secondary component hardly change in the amplitude component and the phase component even if the head is moved to the track adjacent to the track that is currently on-track. However, as the order increases, the eccentricity may change greatly in amplitude component and phase component only by moving the on-track target track to the adjacent track. If the amplitude component or phase component of the eccentricity changes in this way, even if it is possible to follow this change by learning, learning requires several tens of revolutions. There is a possibility that eccentricity correction cannot be performed. In such a case, an appropriate current cannot be supplied to the VCM (voice coil motor) to control the position of the recording / reproducing magnetic head until learning is completed, and as a result, RRO tracking control is performed. However, it becomes impossible to follow the track normally, and it becomes difficult to quickly and accurately position the recording / reproducing magnetic head on the specific track. Therefore, a long time is always required to accurately position the recording / reproducing magnetic head, and the function of high-speed access provided by the HDD is lost. Furthermore, when following different eccentric amplitude and phase components in the on-track trajectory, since the read core trajectory is different when the read core and the write core are positioned on the same track, the RRO following control is performed for each different eccentricity. It is assumed that the read core trajectory and the write core trajectory do not overlap, and the written data cannot be read accurately.

  In order to solve the above problem, when the disk-shaped recording medium is a conventional continuous film, an eccentricity cancellation value table corresponding to each track of the disk-shaped recording medium and the magnetic head for recording / reproducing, for example, eccentricity used in ZAP control The cancel value is recorded as correction information different from the position information in the user area on the disk-shaped recording medium or the specific area of the position information, and high-order RRO correction is performed by an MPU (micro processing unit) or DSP. In this way, the ZAP control is performed so that the stable head position control during the sequential write (sequential write) or sequential read (sequential read) function operation, and the random read or write function operation, or off during the function operation is performed. A method to realize early retry recovery when a truck occurs is proposed And that (Patent Documents 1 to 4). These methods are performed for the purpose of making the orbits of the read core and the write core similar to almost the same perfect circle so that there is no problem in reading and writing data.

JP 2005-92980 A Special Table 2002-54439 Special table 2003-505818 Special table 2003-531451 gazette JP 2005-166115 A JP 2005-166116 A JP 2008-16065 A

  However, the methods described in Patent Documents 1 to 4 are based on the premise that the track width and the track interval are similar to each other in a shape close to a perfect circle. However, as track density increases and DTM / BPM is introduced in the future, a situation in which a similar track shape orbit close to a perfect circle cannot be guaranteed occurs. In that case, the conventional correction method (RRO tracking control method or ZAP control method) that corrects only a portion deviating from a similar orbit close to a perfect circle cannot guarantee read / write operations in all tracks. . Furthermore, since the ZAP control method is limited to the case where the disk-shaped recording medium is a conventional continuous film and has a track-like orbit close to a perfect circle, it cannot be used in DTM, BPM and the like that are expected to be put to practical use in the future.

  HDDs are pursuing higher track density with the aim of increasing capacity, but in order to achieve higher track density, position information is stored on magnetic disk media in order to accurately grasp the track information on which data is recorded. It needs to be formed accurately. For the formation of the position information, a self-STW method in which the apparatus itself writes, a method using a dedicated facility (STW machine) for recording position information, and a method using magnetic transfer using a stamper in which position information is recorded in advance. A method for forming position information in the process of manufacturing a magnetic disk medium is known. This position information is used for the actual position control by correcting the eccentricity component from the center of rotation by performing the eccentricity correction described in the background art on the conventional magnetic disk medium of track density (TPI). However, if the track density is further increased in the future, the conventional correction methods (RRO tracking control method and ZAP control method) will perform accurate position control, that is, the center of the target track on which read / write operations are performed. Therefore, the read core / write core cannot be positioned accurately.

  The reason why accurate position control cannot be performed is a precondition for the conventional correction. Various corrections are implemented with the assumption that all the tracks are almost similar to a perfect circle regardless of the shape. Because. For this reason, it is obvious that accurate position control cannot be performed with the conventional correction technique when a loss of roundness or similar shape that may occur due to high track density occurs. The ZAP control method is based on the premise that the track orbit to be controlled is close to a perfect circle, and the RRO tracking control method is based on the assumption that the track orbit of the track group to be controlled is similar. It is.

  As a medium in which this problem appears remarkably, DTM and BPM in which tracks for writing data are formed in advance are known. In DTM and BPM, the position information is also formed at the time of track formation, so the relationship between the discrete track and the position information is uniquely determined, but each track has a similar shape as close to a perfect circle as possible. Even if it is going to be formed, the process of manufacturing a template for DTM or BPM requires ultra-fine processing, so the time required to create one side of information is set to a few days to a few weeks. It is practically impossible to form a similar-shaped track that is close to a perfect circle due to the situation (temperature change, vibration, etc.). This production time becomes longer as the track density becomes higher. In other words, the template for the discrete track requires ultra-fine processing, and therefore, it is necessary to create it with an ultra-low speed rotation when forming position information. Therefore, there is a possibility that the environment may change greatly at the beginning and end of writing, and also during writing, and since inertial force in the rotation direction can not be expected because position information is written at ultra-low speed rotation, the formed position information is Waviness or the like is written while straying from side to side (radial direction), and swells are imprinted, causing a problem that the roundness and the like are greatly deteriorated depending on the location (circumferential direction and radial direction).

  As a result, the formed track cannot guarantee a track trajectory close to a perfect circle, and the undulation varies depending on the location, so that the similarity between the tracks cannot be guaranteed. In the conventional RRO tracking control method, If the eccentricity correction of the track is to be performed accurately, it is necessary to learn the eccentricity every time the target track changes, and therefore, the high-speed access necessary for the HDD cannot be performed. That is, since it is necessary to perform different RRO follow-up control for each track, the conventional RRO follow-up control method cannot perform high-speed access. Furthermore, the offset correction of the read core and the write core is also caused by this, and when the read core and the write core are positioned on the same target track, the position where the read core exists is different in each, but the eccentricity caused by this different position is different. Therefore, the conventional method having one offset correction value for each track or the method having only one offset correction value for a plurality of tracks cannot cope with the difference in different eccentric components. In this case, when the read core and the write core are positioned on the same target track, the yaw angles of the heads are different from each other, but the amount of change in the amount of eccentricity that occurs due to the difference in the yaw angle is obtained by calculation. In this specification, it is assumed that the correction has been made in advance. A specific implementation method thereof is described in Patent Document 7.

  The present invention has been made to solve such conventional problems, and it is difficult to form a high-track-density magnetic disk medium or a similar-to-perfect track like a DTM / BPM. However, an object of the present invention is to provide an offset correction value measuring method, an offset correction method, and a magnetic disk device to which the method is applied, which can be accurately positioned at the center of a track and can accurately perform a read operation and a write operation.

  The present invention for solving such a problem includes a plurality of tracks formed around the same center of rotation, or a plurality of tracks separated by a nonmagnetic area, and extending in a radial direction across the tracks. In order to read or write data to a track of a magnetic disk medium having a plurality of position information areas in the circumferential direction that divide each track into a plurality of sectors by a magnetic head in which a read core and a write core are separately formed, An offset correction value measuring method for providing offset correction values of the read core and write core for sectors corresponding to all or necessary position information areas, assuming that the track position of the read core is determined in advance. The track corresponding to the necessary or required position information area is While reading the positional information from the information area and performing on-track control, writing the temporary offset measurement data by the write core, and outputting the read data by reading the temporary offset measurement data from the track by the read core A step of detecting a radial position at which the level is maximum and setting a temporary offset correction value; and a step of learning RRO correction information while positioning the lead core at the track center and performing RRO tracking control for the track to be measured Offsetting the read core from the track to be measured by the temporary offset correction value, and executing RRO control according to the learned RRO correction information; and performing the RRO control, In the state corrected with the offset correction value Characterized in that comprises the steps of RO position error value to calculate the offset correction value becomes zero, the.

  In the offset correction value measuring method of the magnetic disk apparatus of the present invention, the RRO position error value is measured while tracking servo control is performed on the offset correction value, and the RRO position error value is frequency-converted from the time domain by discrete Fourier transform. The frequency domain RRO position error value is converted to the position information input to the tracking servo control with the compression characteristics used in the tracking servo control at this time, and the result is converted to the original time domain. It is practical to include a step of calculating a correction value and adding the correction value to the provisional offset correction value.

  Another aspect of the method of measuring the offset correction value of the magnetic disk apparatus according to the present invention includes a plurality of tracks formed around the same rotation center or a plurality of tracks separated by a nonmagnetic area, and intersecting each of the tracks. Thus, data is read by a magnetic head in which a read core and a write core are separately formed on a track of a magnetic disk medium having a plurality of position information areas in the circumferential direction that divide each track into a plurality of sectors. In order to read or write, an offset correction value measuring method for providing offset correction values of the read core and the write core for sectors corresponding to all or necessary position information areas, the track position of the read core being Based on the pre-determined assumptions, tracks corresponding to all or necessary location information areas Then, while reading the position information from the position information area by the read core and performing on-track control, writing the temporary offset measurement data by the write core, and the temporary offset measurement data from the track by the read core The step of detecting the radial position where the output level of the read data is the maximum value is detected and setting a temporary offset correction value, and the lead core is positioned at the track center for the measurement target track while performing RRO tracking control. Learning first RRO correction information, offsetting the lead core from the track that learned the first RRO correction information by the temporary offset correction value, and learning second RRO correction information while performing RRO tracking control, and the read core The first RRO Learning the second RRO correction information while offsetting the temporary offset correction value from the track having learned the positive information and performing RRO tracking control, and the two first and second RROs of the learned track and the offset track The track trajectory when the light core is positioned on each track is calculated from the correction information, and the first and second displacements from the calculated track trajectory, the average position of the measured track and the offset track are calculated. Respectively, calculating the amount, offsetting the lead core from the target track by the temporary offset correction value, executing RRO control according to the learned first RRO correction information, and performing the RRO control, Before the light core is corrected with a temporary offset correction value Calculating an offset correction value for generating a trajectory deviation having a reverse characteristic of the trajectory deviation from the trajectory deviation.

  In the offset correction value measuring method for a magnetic disk apparatus according to the present invention, the step of learning the RRO correction information by positioning the read core on the target track is the step of writing the temporary offset correction value. It can be executed while writing a value. Further, the first and second shift amounts are converted from the first and second RRO correction information into a frequency domain by Fourier transform from the time domain, and the response characteristics in the frequency domain of the tracking servo control target plant at this time It is practical to include the steps of converting to a value output from the plant and converting the result to the original time domain.

  Further, in the offset correction value measuring method of the magnetic disk apparatus of the present invention, the offset correction value is converted from the time domain to the frequency domain by Fourier transform, and used in tracking servo control at this time. The trajectory deviation in the frequency domain is converted into position information at the time when it is input to the tracking servo control with the compression characteristics being used, the result is converted into the original time domain, the correction value is calculated, and the temporary offset A step of adding the correction value to the correction value may be included.

  Further, the offset correction value measuring method of the magnetic disk apparatus according to the present invention from another point of view includes a plurality of tracks formed around the same rotation center or a plurality of tracks separated by a non-magnetic area, A magnetic core in which a read core and a write core are separately formed on a track of a magnetic disk medium having a plurality of position information areas in the circumferential direction, which extend in the radial direction across the track and divide each track into a plurality of sectors. An offset correction value measuring method for providing offset correction values of the read core and the write core with respect to sectors corresponding to all or necessary position information areas for reading or writing data by a head, the write core comprising: Assuming that the track position is determined first, it corresponds to all or necessary position information areas For the rack, reading the position information from the position information area by the read core and writing the temporary offset measurement data by the write core while performing on-track control; and the temporary offset measurement data from the track by the read core And measuring the provisional offset correction value by detecting the radial position where the output level of the read data reaches the maximum value, and positioning the lead core at the track center for the measurement target track and performing RRO tracking control. While learning the RRO correction information, the read core is moved to a radial position where the temporary offset measurement data is read and the output level of the read data becomes the maximum value in the temporary offset correction value measurement. The learned RRO supplement Performing RRO control according to information, and calculating an offset correction value at which the RRO position error value becomes zero in a state where the lead core is corrected with a temporary offset correction value while performing the RRO control. It has the characteristics.

  In this case, the RRO position error value is measured while tracking servo control is performed on the offset correction value, the RRO position error value is converted from the time domain to the frequency domain by Fourier transform, and is used for tracking servo control at this time. The RRO position error value in the frequency domain is converted into the position information input to the tracking servo control with the compression characteristics that are obtained, the result is converted into the original time domain, and the correction value is calculated. It is practical to include the step of adding the correction values together.

  The offset correction value measuring method of the magnetic disk device according to the present invention, which is another mode based on the premise that the track position of the write core is determined first, is the track corresponding to all or necessary position information areas. While reading the position information from the position information area by the read core and performing on-track control, writing the temporary offset measurement data by the write core, and reading the temporary offset measurement data from the track by the read core A step of detecting a radial position where the output level of the read data becomes a maximum value and setting a temporary offset correction value, and for the track to be measured, the read core is positioned at the track center and the first RRO is controlled while performing RRO tracking control. Learning correction information; and Is read out from the track having learned the first RRO correction information by the temporary offset correction value measurement and moved to a radial position where the output level of the read data becomes the maximum value. Learning the second RRO correction information while following control and calculating the track trajectory when the light core is positioned on each track from the first and second RRO correction information of the learned track and the offset track. And calculating the first and second displacement amounts from the calculated track trajectory, the average position of the measured track and the offset track, and positioning the light core on the target track. The target track and the offset offset from the difference between the first and second displacement amounts. Calculating an RRO position error value by calculating a trajectory deviation in the absolute space of the rack; and offsetting the lead core from the target track by the temporary offset correction value to learn the first RRO correction information And executing an RRO control with the offset correction value for generating a trajectory deviation having a reverse characteristic of the trajectory deviation from the trajectory deviation in a state where the light core is corrected with a temporary offset correction value while performing the RRO control. And a step of calculating.

  The step of learning the RRO correction information by positioning the read core on the target track can be performed while writing the temporary offset correction value in the step of writing the temporary offset correction value.

  In the present invention, the first and second shift amounts are converted from the time domain to the frequency domain by Fourier transform from the first and second RRO correction information, and the response characteristics in the frequency domain of the tracking servo control target plant at this time Can be converted to a value output from the plant and the result can be converted to the original time domain.

  In the offset correction value measuring method of the magnetic disk apparatus of the present invention, the offset correction value is further used by converting the orbital deviation from the time domain to the frequency domain by Fourier transform, and used in tracking servo control at this time. The trajectory deviation in the frequency domain is converted into position information at the time when it is input to the tracking servo control with the compression characteristics that are present, the result is converted into the original time domain, a correction value is calculated, and the temporary offset correction value The step of adding the correction values together can be included.

  In the present invention, the offset correction value is a sector unit or a track unit, and a combination of a sector unit and a track unit, and is measured in a state where single or continuous thinning is performed, and the read core for the sector corresponding to the position information area and It is practical that the offset correction value is for the light core.

  The same RRO control correction information is used as RRO control correction information when the read core is on-tracked to the learning target track and when the write core is on-tracked. Is done.

  The offset correction values of the sectors corresponding to all or all necessary position information areas and all or all necessary correction information learned for the RRO control are stored in advance in the storage means of the magnetic disk device. A storing step can be included.

  A step of storing the offset correction values of the sectors corresponding to all or all the necessary position information areas in the storage means of the magnetic disk device in advance, or by interpolation or copying from the thinned offset correction values A step of calculating a necessary offset correction value in advance and storing it in the storage means of the magnetic disk device may be included.

  The storage means is a specific area of the semiconductor memory or the magnetic disk, and it is practical to include a step of writing in the specific area in advance.

  The invention according to the offset correction method of the magnetic disk device including the storage unit in which the offset correction value is written is written on the magnetic disk by the write core on the premise that the track position of the read core is determined first. When performing, the offset correction value corresponding to each target sector to be written is preliminarily read from the storage means, or preliminarily read from the specific area of the magnetic disk by the read core. .

  Further, the present invention, which comprises an apparatus category, is a magnetic disk device comprising a storage means for storing the offset correction value and correction information, on the premise that the track position of the read core is determined in advance. When writing data to the magnetic disk medium, the offset correction value corresponding to the target sector and the correction information learned for the RRO control are read from the storage means to perform offset correction control and RRO control, When data is read from the magnetic disk medium by a magnetic head, a control means is provided for performing RRO control by reading correction information learned for the RRO control corresponding to a target sector from the storage means. Have.

  An invention relating to an offset correction method for a magnetic disk device is an offset correction method for a magnetic disk device comprising storage means for storing the offset correction value and correction information, wherein the track position of the write core is determined first. As a premise, when reading from the magnetic disk by the read core, the offset correction value corresponding to each target sector to be read and the correction information learned for the RRO control are read in advance from the storage means, or in advance The method includes any one of steps of reading from the specific area of the magnetic disk by a read core.

  The invention relating to the magnetic disk device to which the offset correction method is applied corresponds to a target sector when data is read from the magnetic disk medium by the magnetic head on the premise that the track position of the write core is determined first. When the offset correction value and the correction information learned for the RRO control are read from the storage means, offset correction control and RRO control are performed, and data is written to the magnetic disk medium by the magnetic head, the target sector It comprises control means for reading out the correction information learned for the RRO control corresponding to 1 from the storage means and performing RRO control.

  As described above, according to the offset correction method of the present invention and the magnetic disk apparatus that performs the method, the magnetic disk medium having a high track density and the magnetic information having position information that is not close to a perfect circle, such as DTM / BPM, is not similar. In the disk medium, the offset correction values of the read core and the write core corresponding to each piece of position information formed on the magnetic disk medium are independently measured in a short time for all or all necessary tracks. It becomes possible. Moreover, according to the present invention, when measuring the offset value, the offset value of the read core and the write core can be measured without writing formal offset measurement data. The offset correction value can be measured for each track.

1 is a plan view showing a magnetic disk drive device (HDD) to which the present invention is applied with a lid removed. FIG. It is the figure which showed the main member and circuit structure of the HDD with the block. FIG. 4 is a diagram for explaining the yaw angle of a composite MR head in which a read core (read head) and a write core (write head) are separated in an HDD, where (A) is near the outer side, (B) is near the center, C) is a view showing a state in the vicinity of the inner. 2A and 2B are diagrams for explaining how a magnetic head has a yaw angle near the outer periphery of a magnetic disk in an HDD, where FIG. It is a figure explaining RRO follow-up control and ZAP control in HDD. It is a figure showing the track | orbit of the actual magnetic head when RRO tracking control is implemented in HDD. It is a figure showing the track | orbit of the actual magnetic head when ZAP control is implemented in HDD. (A) is a diagram showing a simplified configuration of a read core and a write core of a 10,000 TPI magnetic head, and (B) is a 100,000 TPI magnetic head. (A) is a diagram showing a state in which a 10,000 TPI magnetic head is on-track on a track on which data is written by a 100,000 TPI magnetic head. FIG. 5 is a diagram showing a state in which data used when measuring offset correction values of a read core and a write core is written on a continuous film magnetic disk. FIG. 10 is a diagram showing a state when the read core is offset-seeked in order to measure the offset correction value of the read core and the write core, and just approaches the center of the measurement data. (A) is a diagram showing how the read data for offset measurement is read while the read core 23R is offset-seeked in a predetermined step, and (B) is a graph plotting the output of the read data read out. It is the figure which showed the ideal track | orbit for writing and reading data formed on a magnetic disc. It is the figure which showed the actual track track | orbit by which RRO which is not similar shape was folded on the magnetic disc with the continuous line, and showed the ideal track track | truck with the dotted line. FIG. 5 is a diagram showing a track trajectory in which a similar RRO is folded on a magnetic disk, and a ideal track trajectory indicated by a dotted line. It is the figure which showed the track orbit when the actual high order RRO component of DTM / BPM was removed, and fitted to the ellipse by the solid line, and the ideal track orbit by the dotted line. It is the figure which showed the track orbit when the actual high order RRO component of DTM / BPM was included in the dotted line, and the track orbit when the actual high order RRO component of DTM / BPM was removed and fitted into an ellipse by the solid line. . FIG. 3 is a diagram showing a magnetic disk medium on which an ideal STW is performed, developed linearly starting from a reference servo area. It is the figure which showed the position information example 1 formed simultaneously with DTM / BPM, and expand | deployed linearly from the reference | standard servo area. It is the figure which showed the positional information example 2 formed simultaneously with DTM / BPM, and expand | deployed linearly from the reference | standard servo area. It is the figure which showed the position information example 3 formed simultaneously with DTM / BPM linearly expand | deployed from the reference | standard servo area as the starting point. In DTM / BPM, it is the figure which showed the relationship between the servo area in which the positional information is formed, and the track in which data are written. It is the figure which showed the result of having performed desirable offset correction. In Example 1 and Example 2 of offset measurement, temporary data for measuring offset correction values of the read core and the write core in a state where the read core is on-tracked to the track No. 4 of the measurement target track after performing the full erase. It is the figure which showed a mode that (temporary measurement data) was written. In the offset correction value measuring method of the present invention, the magnetic disk surface is shown linearly developed from the reference servo area as a starting point, showing the time point when learning of the RRO correction information of the track for measuring the official offset value is completed. FIG. In the embodiment of the offset measurement of the present invention, the magnetic disk surface is linearly developed from the reference servo area as a starting point, showing a state in which the relative offset of the average read core and write core measured in FIG. 24 is corrected. FIG. In the embodiment of the offset correction value measuring method of the present invention, it shows a state where the write core is corrected by the average offset value for one round measured in FIG. It is the figure expanded and shown. In the embodiment of the offset correction value measuring method of the present invention, it shows a state when the on-track control is performed using the offset correction value at which the position error becomes zero. FIG. In the second method of measuring the offset correction value using the RRO tracking control of the present invention, the magnetic disk surface is linearly developed starting from the reference servo area indicating the time point when the learning phase of the first RRO correction information is completed. FIG. In the second method of measuring the offset correction value using the RRO tracking control according to the present invention, the magnetic disk surface is linearly developed starting from the reference servo area, which indicates the time when the learning of the second RRO correction information is completed. FIG. In the second method of measuring the offset correction value using the RRO tracking control of the present invention, in order to accurately position the write core on the target track No. 4, it is learned and stored when the read core is positioned on the track No. 4. A magnetic disk showing a state in which tracking servo control is performed on the result of adding the correction value Dn to the position information obtained by demodulating track No. 2 while performing the RRO control using the RRO correction information An It is the figure which expanded and showed the surface linearly from the reference servo area as the starting point. It is the figure which showed the flow of Example 1 of the offset correction value measuring method of this invention with the flowchart. It is the figure which showed the flow of Example 2 of the offset correction value measuring method of this invention with the flowchart. (A) is a diagram showing a NULL servo pattern, and (B) is a graph showing an example 1 of offset measurement data read output, to which the present invention is applied. (A) is a phase servo pattern, and (B) is a graph showing an example 2 of offset measurement data read output to which the present invention is applied.

  The present invention will be described with reference to the embodiments shown in the accompanying drawings. FIG. 1 is a plan view showing an HDD to which the present invention is applied with a lid removed, and FIG. 2 is a block diagram showing main members and circuit configuration of the HDD. In this embodiment, DTM is used as the magnetic disk medium.

  The HDD 10 includes a disk enclosure (DE) 11 and a circuit board (PCA) 12. In the disk enclosure 11, a magnetic disk (magnetic disk medium) 21, a spindle motor (SPM) 22, a magnetic head (Head) 23, a carriage arm 24, a voice coil motor (VCM) 25, and a preamplifier 26 are housed. . The magnetic disk 21 is fixed to the spindle shaft of the spindle motor 22 and is driven to rotate in the magnetic disk rotation direction θ indicated by the arrow by the spindle motor 22.

  The magnetic head 23 includes a read core 23R and a write core 23W independently. The read core 23R and the write core 23W are arranged to face the magnetic disk 21 and magnetically act on the magnetic disk 21 to record or record information. Perform playback. The magnetic head 23 is attached to the tip of a carriage arm 24 that is pivotally supported. The carriage arm 24 is mounted with a voice coil of a voice coil motor (VCM) 25 at the other end, and can be rotated in the direction of the arrow φ by the VCM 25. As the carriage arm 24 rotates in the arrow φ direction, the magnetic head 23 moves in the radial direction of the magnetic disk 21, that is, in the arrow φ direction.

  The magnetic head 23 is connected to the preamplifier 26. The preamplifier 26 amplifies a signal to be recorded on the magnetic disk 21 by the magnetic head 23, supplies the signal to the magnetic head 23, and amplifies a reproduction signal reproduced from the magnetic disk 21 by the magnetic head 23, Supply.

  The circuit board 12 includes a read channel (RDC) 31, a MPU (Micrio Processing Unit) 32, a flash ROM 33, a servo controller (SVC) 34, a hard disk controller (HDC) 35, and a RAM (RAM). Random Accees Memory) 36 and an interface connector 37 are mounted. The MPU 32 includes a DSP (Digital Signal Processor) function. Further, the MPU 32 may be entirely replaced with a DSP to include the functions of the MPU.

  The read channel 31 is connected to the preamplifier 26, supplies a recording signal to the preamplifier 26, and demodulates the reproduction signal amplified by the preamplifier 26 into reproduction data. The reproduction data demodulated by the read channel 31 is supplied to the hard disk controller 35. The hard disk controller 35 temporarily stores the reproduction data in the RAM 36 and then supplies it to a host computer (not shown) via the interface connector 37. At this time, the reproduction data read by the magnetic head 23 (read core 23R) and demodulated by the read channel 31 is also supplied to the MPU 32.

  The hard disk controller 35 temporarily stores recording data supplied from the host computer via the interface connector 37 in the RAM 36, reads out from the RAM 36 during recording, and supplies it to the read channel 31. The read channel 31 modulates recording data from the hard disk controller 35 to generate a recording signal. The recording signal modulated by the read channel 31 is supplied to the preamplifier 26. The preamplifier 26 amplifies the recording signal from the read channel 31 and supplies it to the magnetic head 23. The magnetic head 23 (write core 23W) generates a magnetic field corresponding to the recording signal from the preamplifier 26, magnetizes the magnetic disk 21, and records (writes) the recording signal on the magnetic disk 21. At this time, reproduction data read by the magnetic head 23 (read core 23R) and demodulated by the read channel 31 is supplied to the MPU 32.

  The MPU 32 reads position information on the magnetic disk 21 from the reproduction data, that is, position information (track (Tr) No., sector No. and burst servo signal) from the servo area, and performs on-track control. The MPU 32 generates a control signal, that is, a position error signal according to the difference between the read position information and the position where the target data is stored or the position information of the position for storing the target data. The servo controller 34 drives the VCM 25 to perform on-track control of the magnetic head 23 at the tip of the carriage arm 24.

  In addition to the program data for controlling the MPU 32, the flash ROM 33 supplies correction values for correcting the read position information (offset correction values for the read core and write core, position information replacement table, etc.) and the servo controller 34. Correction values (such as RRO correction information and ZAP control values) for correcting the position error signal to be corrected are stored in the position correction information storage area 38. These correction values are correction values that are necessary for making the trajectory of the write core 23W coincide with the trajectory of the read core 23R when the recording data is read when the recording data is written on the magnetic disk 21. When reading data, the correction value is used for causing the read core 23R to accurately follow the track on which the data on the magnetic disk 21 is recorded. Therefore, correction values corresponding to the write core 23W and the read core 23R are read from the position correction information storage area 38 in accordance with writing and reading, and are used for on-track control correction.

  The servo controller 34 controls the VCM 25 based on a control signal (position error signal) from the MPU 32, and controls the reading position of the signal from the magnetic disk 21 by the magnetic head 23.

  As described above, the magnetic head 23 scans the target position on the magnetic disk 21, and information can be acquired and information can be recorded.

  FIG. 3 is a diagram for explaining the yaw angle of the composite MR head in which the read core 23R (read head) and the write core 23W (write head) are separated. The magnetic head 23 attached to the HDD swing type carriage arm 24 of the HDD has a positional relationship between the read core 23R and the write core 23W according to the position where the magnetic head 23 is positioned by the rotation of the carriage arm 24. There are three types of states, such as near, (B) center, and (C) near the inner. A magnetic head that is currently in practical use is known in which the read core 23R has a head width of about 65 nm, the write core 23W has a head width of about 90 nm, and a head-to-head gap length HG of about 4 μm.

  In the case of the magnetic head 23 as described above, when positioned near the center of the magnetic disk 21 (in the radial direction), the positional relationship between the read core 23R and the write core 23W is in the magnetic disk rotation direction θ indicated by the thick arrow. Since it is linear, it can be positioned at the same position during both reading and writing. On the other hand, when the magnetic head 23 is positioned near the inner side and the outer side of the magnetic disk 21, the positions of the read core 23R and the write core 23W are different from each other in the rotational direction θ. At the time of writing and at the time of writing, the position of the magnetic head 23 is shifted so that the read core 23R at the time of reading and the write core 23W at the time of writing are positioned at the same position on the magnetic disk 21 (yaw angle correction, offset correction). There is a need to. This yaw angle is uniquely determined by the rotational position of the carriage arm 24 on which the magnetic head 23 is mounted.

  FIG. 4 shows a state in which the yaw angle near the outer is attached. At the time of writing operation (at the time of writing operation), the write core 23W is on-tracked on the target data writing track, and data is written (FIG. 4A). During the read operation (read operation), the read core 23R is on-tracked on the track in which the target data is written, and the data is read (FIG. 4B). In the figure, hatched portions are write data WD and read data RD. Correction of the positions of the read core 23R and the write core 23W is yaw angle correction or offset correction. In FIG. 4A, correction for the yaw angle correction amount Δφ is necessary.

  FIG. 4 shows a case where the width of the read core 23R and the width of the write core 23W is about ½ of the gap between the heads. However, in the case of the example of the magnetic head 23 described in FIG. In the state with the yaw angle as shown in FIG. 4, there are several tens of data tracks between the read core 23R and the write core 23W.

"RRO tracking control and ZAP control"
FIG. 5 is a diagram illustrating RRO tracking control and ZAP control, and is a plan view showing ideal complete circular tracks 200 and 201 and actual tracks 202 and 203 on the magnetic disk surface 21a. The magnetic disk surface 21a includes a plurality of spoke-shaped servo areas (SA) 300, 301,. Actually, several hundred or more may be provided, but they are omitted in the figure. Each servo area (SA) 300, 301,... Is formed at substantially equal intervals in the circumferential direction, and divides each track 202, 203 into a plurality of sectors (data area (DA)). The area between the servo areas (SA) 300, 301,... Is a data area DA for writing and reading data. Position information corresponding to the divided areas of the tracks 202 and 203 is recorded in the servo areas 300 and 301. The position information includes the actual positions of the tracks 202 and 203 (radius) along the magnetic disk surface 21a. Track information or cylinder information, which is a direction position), and servo information indicating a position in the track. In this embodiment, servo information of so-called four burst servo patterns (bursts A to D) is written in the servo areas 300 and 301 in advance. Each servo area 300, 301 is formed continuously (as a continuous film) in the radial direction.

  All position fluctuations away from the circular tracks 200 and 201 are considered as position errors. The portions of the tracks 202 and 203 that do not follow the circular tracks 200 and 201 generate a reproducible RRO (repeatable run-out) error written at the time of servo track write (STW). A position error when the same error occurs every time the magnetic head 23 passes a specific position on the magnetic disk surface 21a is considered as an RRO position error. This is because whenever the magnetic head 23 follows the servo areas 300, 301 that define the radial position of the tracks 202, 203, it produces the same positional error relative to the ideal circular tracks 200, 201. Because it does.

  The main cause of the positioning error of the magnetic head 23 is a reproducible disturbance caused by the spindle motor 22 and an embedded servo formed during writing by a servo track write (STW) or a manufacturing process such as DTM / BPM. RRO position error caused by a trajectory deviating from an ideal trajectory (perfect circle) such as a disc-shaped recording medium center axis deviation at the time of signal formation and mounting of the disc-shaped recording medium to the disc drive device is there. Several methods have been proposed to deal with this reproducible disturbance. These methods can be classified into two groups.

  The first group is called repetitive control using DFT (Discrete Fourier Transform) and RRO correction of adaptive feedforward correction. It accurately tracks disturbances caused by spindle motors and tracks 202 and 203 written by STW. I am trying to trace. For this reason, any track such as a spindle motor can be dealt with in the same way, so that accurate follow-up is possible. Further, regarding the RRO error caused by the STW, it is possible to follow the trajectory having a unique shape generated after the STW process such as the tracks 202 and 203. The first group described here is called RRO tracking control.

  The second group relies on the concept of zero acceleration path (ZAP (Zero Acceleration Path)) (referred to as “reproducible run-out correction”). It is a non-adaptive feedforward technique for correcting RRO in front of the feedback controller.

  The concept of ZAP control will be described with reference to FIG. In FIG. 5, tracks 202 and 203 represent track centers after the STW process. Due to various disturbances that occur during the STW process, the center of the track exhibits a trajectory that is not ideally smooth and difficult to follow by an actuator. As a result, a reproducible position error signal is generated. However, when an appropriate correction amount is subtracted from the position measurement signal in each servo area, the original zigzag path becomes smooth. That is, the center of the track becomes an ideal circle like the tracks 200 and 201. If the disturbance to the non-reproducible position information is negligible, the center of this ideal circular track 200, 201 can be followed by the ZAP (zero acceleration path) technique. The second group described here is called ZAP control.

"Prerequisites for RRO tracking control"
FIG. 6 is a diagram illustrating the trajectory of the magnetic head 23 when the RRO tracking control is performed. In the RRO tracking control, the same correction value is used for a plurality of correction target tracks, for example, the tracks 202 and 203. The correction values here are correction orders (single or plural) and gains and phases of those orders. Therefore, the eccentric orders existing in both of the tracks 202 and 203 and whether they have the same gain and the same phase are determined, and control is performed so as to follow only the orders. When the orders common to the tracks 202 and 203 are only the first, second, third, and fifth orders, control is performed so as to follow only these four kinds of eccentric orders. Other orders differ from track to sector and are therefore excluded from the control target. The trajectory traced by the magnetic head 23 when the RRO tracking control is performed is shown as RRO tracking tracks 206 and 207. Further, the RRO tracking control is generally used while constantly learning the RRO state and updating the RRO correction information, such as adaptive feedforward correction.

  As described above, the reason why the control target order is selected is to prevent a different trajectory for each track / sector. If different trajectories are used, the on-track of the read core 23R and the on-track of the write core 23W will pass different trajectories at the respective on-track positions (in the case of the read core reference). And the light core 23W will not pass through the same track. As a result, it is assumed that the recorded data cannot be read accurately. In order to avoid this, the order of the RRO tracking control target is limited to only the order common to the track of the RRO tracking control target.

"Preconditions for ZAP control"
FIG. 7 shows an actual trajectory when the ZAP control is performed. As a result of the ZAP control, the magnetic head 23 passes along an orbit close to an ideal perfect circle like the ZAP control tracks 208 and 209. Since all tracks to be subjected to ZAP control have a trajectory close to a perfect circle, it is not necessary to consider interference between adjacent tracks. This indicates that all orders (up to the Nyquist frequency) can be targeted as long as there is no inconvenience regarding the order of the ZAP control target. The inconvenience here refers to a state in which the amplitude and phase are constantly fluctuating. That is, in the ZAP control, when the control is executed, all the tracks to be controlled are track tracks that are close to a perfect circle. Therefore, the on-track positions of the on-track of the read core 23R and the on-track of the write core 23W (read core reference) In this case, the trajectory is almost the same shape. Therefore, by correcting only the offset values of the read core 23R and the write core 23W, the read core 23R and the write core 23W can be easily positioned on the target track.

"Relationship between magnetic head and track density (TPI)"
FIG. 8 shows a simple configuration of the read core 23R and the write core 23W of the magnetic head 230 compatible with 10,000 TPI and the magnetic head 231 compatible with 100,000 TPI. 8A shows the magnetic head 230, and FIG. 8B shows the magnetic head 231. It can be seen from these figures that the relationship between the read core 23R and the write core 23W (the gap length HG between the heads) hardly changes even when the track density increases and the track pitch (corresponding to the head core width HW) decreases. Show. Actually, the gap length HG between the heads has an error of about ± 1 μm due to the characteristics of each magnetic head, but does not change greatly. On the other hand, the track density becomes a larger value as long as the magnetic disk device aims to increase the density / capacity. That is, in the future, it is shown that the track pitch of the magnetic disk medium becomes narrower and the track density becomes higher while the gap length HG between the heads of the magnetic head is fixed. Note that 10,000 TPI has a track pitch of about 2.5 μm, and 100,000 TPI has a track pitch of about 0.25 μm (about 250 nm).

"Relationship between magnetic head and track"
FIGS. 9A and 9B show a state in which the magnetic heads 230 and 231 are on-track on a track to which data is written. In FIG. 9, the shaded area represents the track data area. The two types of magnetic heads 230 and 231 have the same yaw angle, but the magnetic head 230 has a positional relationship between the read core 23R and the write core 23W of about 0.5 track, whereas the magnetic head 231 This gap has expanded to 5 tracks. That is, as the track density increases, the number of tracks existing between the read core 23R and the write core 23W increases in proportion thereto. At present, HDDs that are actually put into practical use have a high track density up to about 250,000 TPI, and the track pitch is narrowed down to about 100 nm. In this case, in the magnetic head 23 shown in the figure, there are about 13 tracks between the read core 23R and the write core 23W. Accordingly, the offset correction value for correcting the offset between the read core 23R and the write core 23W is a value that needs to be corrected for ten to several tens of tracks.

  The above example assumes that the read core 23R and the write core 23W are linearly aligned when the yaw angle is zero. However, depending on the manufacturing status of the magnetic head, there is an offset when the yaw angle is zero. There are also things. In the case of a magnetic head having such an offset, the offset becomes 0 when a certain yaw angle is provided, and therefore the offset correction value is set with reference to the position where the offset is 0. Furthermore, among actual magnetic heads, there are magnetic heads that do not overlap linearly at any position from the inner zone to the outer zone. In that case, a position where the temporary offset correction value is 0 is provided outside the zone, and the offset correction value is set based on the position.

  A method for measuring the offset correction value will be described with reference to FIGS.

"Write offset measurement data"
FIG. 10 is a diagram showing a state in which data (offset measurement data) used when measuring the offset correction values of the read core 23R and the write core 23W is written on a continuous film magnetic disk. In the figure, the broken line in the vertical direction represents the track center TrC, and shows that the read core 23R is positioned at the center of the track (Tr) No. 0 and the offset measurement data is written by the write core 23W in that state. . In this embodiment, the write core 23W is located in the outer half area of the track No.1. In the figure, each group indicated by six bold lines represents a burst A to D of the servo pattern written in the servo area, and data is written into the data area and read out from the data area. In FIG. 10, the area where the bursts A to B are written is the servo area SA, and the area following the servo area SA is the data area DA where data is written and read. A solid line parallel to the track center TrC represents each track boundary TrB, and between the track boundary TrB and the track boundary TrB represents a discrete track (magnetic region), and a broken line region on the track of the write core 23W is offset measurement. This shows a state in which write data for writing is written. The same applies to the following figures.

"Read offset measurement data"
FIG. 11 shows the state when the read core 23R is offset-seeked to measure the offset correction values of the read core 23R and the write core 23W, and the read core 23R has just approached the center of the offset measurement write data. .

  FIG. 12A shows how the read data for offset measurement is read while the read core 23R is offset-seeked in a predetermined step, and FIG. 12B is a graph plotting the output level of the read data (read data). Show. In the graph, the vertical axis indicates the output level of the read data, and the horizontal axis indicates the track position where the read core 23R is positioned by performing an offset seek.

  This graph shows that the track position when the output of the read data becomes the maximum is the offset correction value of the read core 23R and the write core 23W. In other words, the write data for offset measurement is written by the write core 23W while the read core 23R is tracing the center of the track No. 0, but the maximum output obtained when the write data for offset measurement is read by the read core 23R is the maximum output. Since it is the position of 0.75 track, the calculation of 0.75-0 = 0.75 is valid. Therefore, the offset between the read core 23R and the write core 23W of the magnetic head 23 is equivalent to 0.75 tracks.

  In the conventional actual HDD, the measurement as described above is performed in each sector. For example, assuming that the track circumference is divided into 200 sectors, the measurement is performed in each 200 sectors, and the measurement results are averaged to calculate the offset correction value of the measurement target track.

  The description so far is the method of measuring the offset correction value when a continuous film magnetic disk is used, but the offset correction value can be measured by the same method in DTM and BMP. However, in the case of DTM or BPM, since the non-magnetic part exists on the magnetic disk, it is necessary to perform measurement in consideration of the non-magnetic part. 5 and Patent Document 6.

"Ideal track trajectory for recording magnetic disk data"
FIG. 13 shows an ideal track trajectory formed on the magnetic disk surface 21a for writing and reading data. In the drawing, six ideal track trajectories 210 to 215 are shown as ideal track trajectories in a simplified manner, and 16 servo areas 300 to 315 are defined with 16 sectors and servo areas (spokes) for one track. It is shown.

“Actual track trajectory (ZAP control) for recording magnetic disk data”
FIG. 14 shows track trajectories (solid lines) 210 to 215 when on-track control is performed using position information read from the magnetic disk as it is, and track trajectories (dotted lines) 210 to 215 as a result of applying ZAP control. Represents. When the ZAP control is performed, the RRO component of the track trajectory is canceled when the position information is detected and input to the servo controller 34. Therefore, the servo controller 34 considers that an ideal track trajectory such as a dotted line has been input. Works. Therefore, ideal track trajectories (dotted lines) 210 to 215 are drawn even as a result of actual on-track control, and the dotted ideal track trajectories 210 to 215 approach the perfect circle of the ideal track trajectory in all the trajectories. . As a result, even in the magnetic head 23 in which the read core 23R and the write core 23W are independently formed, the orbit of the read core 23R and the orbit of the write core 23W draw a similar circle with different radial positions. When the correction is performed so that the read core 23R and the write core 23W pass through the same track, it is only necessary to have an offset correction value uniquely determined corresponding to each yaw angle position.

“Actual track trajectory for recording data on magnetic disk (RRO tracking control)”
FIG. 15 shows ideal track tracks (dotted lines) 210 to 215 in which similar RROs are folded. In this way, the RRO tracking control corrects only the RRO component that can pass the same trajectory in any track. The RRO follow-up control uses the input position information as it is for on-track control, and forcibly follows a portion deviating from the ideal track trajectory (dotted line) 210 to 215 because the RRO component is superimposed on the track. This is performed by outputting an instruction value for performing in addition to the on-track control value output to the servo controller 34. As a result, all track trajectories draw the same similar trajectory (solid line). Therefore, the solid track trajectory approaches the similar trajectory in all the track trajectories. As a result, even in the magnetic head 23 in which the read core 23R and the write core 23W are independently formed, the orbit of the read core 23R and the orbit of the write core 23W draw a similar orbit with different radial positions. Therefore, when correction is performed so that the read core 23R and the write core 23W pass the same trajectory, it is only necessary to have an offset correction value uniquely determined corresponding to each yaw angle position.

"Track trajectory excluding high-order RRO components of DTM / BPM"
FIG. 16 shows a track trajectory when an actual high-order RRO component of DTM / BPM is removed and fitting into an ellipse. The track trajectories 210 to 215 represented by dotted lines indicate ideal perfect circular trajectories (in the figure, ellipses), but in the DTM / BPM, the track trajectories 210 to 215 represented by solid lines differ from track to track. Draw a shape trajectory. FIG. 16 shows an elliptical orbit, and shows that the position where the elliptical orbit is crushed differs for each track. This is due to the fact that the effect of inertial force cannot be expected at all because the rotational speed when the track trajectory is formed by DTM / BPM is extremely low. During STW for forming a normal track orbit, writing is performed while rotating the magnetic disk at a high speed of several thousand to 15,000 revolutions per minute. For this reason, a track trajectory can be formed in a short time, and an inertial force can be expected.

  Although DTM / BPM is described here, if the track density is further increased, even if STW is performed at high speed rotation, it is easily estimated that the track will be different for each track. . Therefore, even with a continuous film magnetic disk, the same problem may occur if the track density becomes higher.

  On the other hand, as described above, in DTM / BPM, it is necessary to form a master medium, a DTM / BPM pattern mask, etc. (not described in the disclosure of the present invention) necessary in the manufacturing process of the magnetic disk medium. The time is long, and usually several days to several weeks are required, and the track trajectory deviates from a perfect circle in the process of forming the track trajectory. Although this figure is described as an ellipse, in reality, it is a track orbit of various shapes, such as a triangle, an oval, or a rounded corner of a rectangle. Furthermore, the problem is that if the track trajectory is, for example, an ellipse, it can be handled by RRO tracking control if it is an ellipse that faces the same direction at any radial position. However, the direction in which the ellipse is crushed may be different for each formed track orbit. Therefore, in the conventional method in which the same order RRO follow-up control is performed from the inner to the outer, it is necessary to learn over time each time when moving from one track to another. A further problem is that when the position of the read core 23R and the position of the write core 23W are offset, the radial position for tracking the track is different when the cores 23R and 23W are positioned. When the tracking control is performed to completely follow the track trajectory, the actual track trajectory through which the read core 23R and the write core 23W pass is different. Therefore, the conventional adaptive feedforward correction method RRO tracking control cannot be used.

  The learning here means learning of the RRO generated at that time in the operation actually performed in the general RRO tracking control of the adaptive feedforward correction method. In the description of the RRO component so far, RRO tracking control has been made possible because it is the same for any track. However, the RRO component of an actual general HDD is not the same for any track in a strict sense. Although it is within the allowable range, a minute change occurs when the tracks are different. It is known that this difference is small between adjacent tracks and large between distant tracks. In order to absorb this difference, learning is always performed in general RRO tracking control. However, since the learning content is not a feature of the present invention, a detailed description thereof is omitted.

“Track tracks including high-order RRO components of DTM / BPM”
FIG. 17 shows a track trajectory including the actual higher-order RRO component of DTM / BPM. In the actual track trajectory, the low-order RRO component forms an elliptical or triangular or egg-shaped trajectory, and the high-order RRO component forms a unique shape for each track trajectory.

  In the case of DTM / BPM, it is necessary to completely trace the track trajectory formed on the magnetic disk medium. In the case of a continuous film magnetic disk, it was possible to determine at the time of writing the first write data after assembling the HDD at the factory so that the track trajectory is most easily written when actually writing data, but DTM / BPM However, since the track trajectory in which data can be recorded is determined in advance, it cannot be determined freely after the HDD is assembled. Therefore, on-track control that can accurately trace the track trajectory formed on the magnetic disk is required. For this, RRO follow-up control is effective, but the conventional adaptive feedforward correction method RRO follow-up control alone cannot sufficiently satisfy the requirements.

  Further, with respect to offset correction of the read core 23R and the write core 23W, it can be seen from FIGS. 16 and 17 that accurate correction cannot be performed with the conventional correction method with one correction value for the target track. That is, when the shape of the track trajectory for one rotation is greatly different for each track trajectory and the offset between the read core 23R and the write core 23W is one track or more away, the position of the read core 23R and the write core 23W However, since the conventional offset correction method has only one correction value for the track trajectory of one rotation, the distortion generated in the position information of the on-track control target is absorbed. The situation is impossible.

"Ideal location information"
FIG. 18 shows a linear development of the state of the surface of the magnetic disk medium on which ideal STW is performed, starting from the reference servo area 300. The servo areas 300 to 308 are areas indicating position information, and the vertical stripes at equal intervals in the figure represent a scale indicating the distance between tracks. The fact that the graduations are equally spaced indicates an environment in which an accurate position without distortion can be measured. In this figure, since the position information is regarded as a ruler for measuring the length, it is shown that the measurement result of the ruler is accurate in the case of equal intervals. If the interval between the vertical stripes of the scale is extended or reduced, this indicates that the measuring ruler is distorted. That is, when the interval is wide, the measured length is shorter than the actual length, and when the interval is narrow, the measured length is longer than the actual length.

  The microscopic STW used in an actual HDD, when viewed microscopically, has an interval corresponding to the vertical stripes in the servo areas 300 to 308 extending or contracting, but since the change is small, it can be ignored so far. It was. However, in the case of DTM or BPM, since the position information is formed in a state where STW is performed at ultra-low speed rotation, an ideal STW as shown in FIG. 18 cannot be performed. For this reason, there is a problem that distortion is superimposed on the measured position information, and accurate position control cannot be performed. Therefore, it is necessary to remove this distortion. In FIG. 18, the double vertical line indicates the center TrC of the track from which data is read or written. Although the actual servo areas 300 to 308 are very narrow, in FIG. 18, the width in the rotation direction (circumferential direction) is shown wider than the actual width in order to facilitate explanation.

  An embodiment of the invention relating to the offset correction method will be described with reference to FIGS.

“Examples 1, 2, and 3 of position information formed simultaneously with DTM / BPM”
19, 20 and 21 show examples 1, 2 and 3 of position information formed simultaneously with DTM and BPM. FIG. 19 shows the case where the degree of eccentricity is the same but the phase is shifted for each track. FIG. 20 shows the case where the degree of eccentricity is the same but the amplitude changes for each track. Each of them represents a different eccentric order or phase. These differences in phase shift, amplitude change, and eccentric order are due to the long time required to form the position information for each track. In actual DTM and BPM, since these are intertwined in a complicated manner and track position information is formed, a more complicated track trajectory is formed. For this reason, due to the above cause (the formation of positional information for each track takes a long time), the eccentric component differs for each track, and the conventional RRO follow-up control cannot be applied. That is, the conventional RRO follow-up control is based on the premise that the same eccentricity is generated in any track, and therefore cannot be dealt with in an environment where the eccentric component is different for different tracks. Even if it can be dealt with, since the track resulting from the RRO tracking control for each track is different, the lead core 23R and the write core 23W are located on different tracks (when the yaw angle is attached). The on-track trajectory is different, and even if the centralized offset correction as in the past is performed, data cannot be written or read at an accurate position.

“Relationship between DTM and BPM track position and position information”
FIG. 22 shows a relationship between an area (servo area) where position information of DTM / BPM is formed and a discrete track (magnetic area, data area) in which data is written. Each discrete track to which data is written is magnetically separated from the adjacent discrete track by a nonmagnetic area. Further, as shown in this figure, in the DTM / BPM, the center TrC of the discrete track and the center of the position information (burst A, B) are the same, and the center of the read core 23R is the center of the position information. If it matches, the center TrC of the discrete track is automatically matched. Therefore, when reading data, the read core 23R center can be accurately read out by aligning it with the center of the position information (burst A, B). However, when data is written, the read core 23R center remains as shown in FIG. Then, since the write core 23W is not positioned at the center TrC of the discrete track, accurate data cannot be written. Therefore, when data is written by DTM or BPM, offset correction is performed so that the position of the write core 23W is accurately positioned at the center TrC of the discrete track. In FIG. 22, the broken line region described overlapping the track boundary TrB represents a nonmagnetic region. The same applies to the following drawings.

"Offset correction results of the present invention"
FIG. 23 shows the result of offset correction according to the embodiment of the present invention. Track No. 4 in FIG. 23 shows a state in which the write core 23W accurately traces the actual track center TrC of DTM or BPM. For this purpose, this embodiment does not use the offset correction values of the read core 23R and the write core 23W, which are averaged over one track of the conventional track, but treats each servo area on the track as an independent event. Measure the offset correction values of the read core 23R and the write core 23W in each servo area, and use them as correction values for each servo area to enable accurate positioning of the write core 23W as shown in FIG. did. As a result, write data can be accurately written to the center TrC of the discrete track.

  In FIG. 23, a region filled with a broken line represents a non-magnetic region (track separation band), and a region sandwiched between non-magnetic regions (track separation band) represents a discrete track. Thus, a straight line passing through the approximate center of the discrete track represents the ideal track center TrCa, and a double line represents the actual track center TrCb. A region represented by a bold line in a horizontal stripe represents write data. Reference numerals 300 to 308 denote servo areas formed in the radial direction, and an area where the servo areas 300 to 308 intersect the discrete track is an area (servo area SA) where a position signal is output. The same applies to the following drawings.

“Example of offset correction value measurement using RRO tracking control”
A method for measuring the offset correction value using the RRO tracking control of the present invention will be further described with reference to FIGS. FIG. 32 is a flowchart showing the flow of the offset correction value measurement method. The following offset correction value measurement method and the like are implemented under the control of the MPU 32 after the power is turned on, and the measurement values and the like are written in either the semiconductor memory (flash ROM 33 or RAM 36) of the PCA 12 or the data storage area of the HDD 10. Read out and used. The present invention can also be implemented under the control of a host computer (not shown) connected via the interface connector 37. In this case, the measurement value or the like can be written to a storage medium in the host computer, and the written measurement value or the like is read and used.

(1) Temporary Offset Measurement Data Writing Stage FIG. 24 shows the read core in a state where the read core 23R is on-tracked to the track No. 4 which is the measurement target track after performing full erase on the magnetic disk surface 21a. It has been shown that temporary data (temporary offset measurement data) for measuring offset correction values of the 23R and the write core 23W is written by the write core 23W. This figure shows a state in which temporary offset measurement data is written to an average track center TrC without performing RRO correction. In this step (1), since it is only necessary to know the rough offset correction values of the average read core 23R and write core 23W, the average value for the entire circumference of the track to be measured may be measured as in the prior art.

(2) Temporary offset measurement data reading stage After writing the temporary offset measurement data, the written data is read to find the on-track position of the read core 23R where the output level is maximized. In this embodiment, since the magnetic head 23 is used at the yaw angle position where the write core 23W is offset by about 2 tracks in the inner direction with respect to the read core 23R, the write data is written in the vicinity of the track No. 6. It is. Therefore, the read core 23R (magnetic head 23) is step-seeked from the writing position (near track No. 4) in the inner direction, the read data is read by the read core 23R, and the radial position where the maximum value (peak value) is obtained is detected. To do. In this embodiment, the read output level becomes maximum (maximum output) near the center TrC of track No. 6. From the seek result, (maximum output position) − (data writing position) = 2, and it can be seen that the write core 23W is offset in the inner direction of about two tracks with respect to the read core 23R. In this embodiment, the average offset correction value for correcting the two tracks in the inner direction is a temporary offset correction value for the write core 23W.

  In FIG. 24, a plurality of read cores 23R and write cores 23W are written. These are read cores 23R and write cores when the magnetic head 23 is sought in the inner direction and the servo areas 300 to 308 are crossed. For convenience, the position of 23 W is shown for each servo area 300 to 308 at each timing. This method is the same for other figures.

  In this embodiment, it is described that the temporary offset measurement is performed on all the tracks to be measured. However, as described above, as long as the measurement accuracy permits, only a specific track, for example, the outermost center, the center, and the like are measured. And the innermost three measurements, and the result may be interpolated or applied to a polynomial to obtain a temporary offset correction value for each track.

  Then, the process after step (3) regarding the measurement of the offset correction value using RRO tracking control is executed. The details will be described below.

(3) RRO Correction Information Learning Stage FIG. 25 shows a point in time when the learning stage of the RRO correction information of the track for which the official offset correction value is measured is completed. In this figure, in order to measure the offset correction value of track No. 4, the read core 23R is made on track in track No. 4 to learn the RRO correction information, and the end point is shown.

  The learning of the RRO correction information is performed while the read core 23R is positioned at the center TrC of the offset measurement target track and RRO tracking control is performed. The offset measurement target track in FIG. 25 is track No. 4. Under the above-described conditions, the read core 23R is positioned at the center TrC of each track, and all the RRO orders that need to be corrected are learned while confirming the generated RRO (position quality, position error amount). An end condition is determined in advance so that the learning of the RRO correction information is ended when the generated RRO is reduced to a predetermined value or less. The RRO order that needs to be corrected is determined by confirming (reading) the entire track to be measured in advance and confirming whether or not the occurrence of RRO exceeding a predetermined value is observed. If any track exceeds the standard, all tracks will be corrected. The order conditions to which the RRO follow-up control cannot be applied are the order in which the amplitude and phase of the RRO change every moment, the order in which the amplitude and phase change due to temperature change, and the dynamic range of the amplitude. Is any one or more of the orders exceeding.

  The specific condition for the end of learning at this time is, for example, a condition that the fluctuation of the position of the lead core 23R is within a certain range from the track center TrC, for example, a predetermined probability (for example, 10 times measurement). If all 10 conditions are satisfied), it is determined that, for example. Alternatively, a condition may be used in which the learning is terminated as it is when the number of learning is simply set to a predetermined number, such as 10 or 20, and learning is completed for this number of times. In this case, the end condition is not the position fluctuation but the number of measurements. As described above, learning is performed in units of tracks until some predetermined condition is satisfied, and when learning of all the target tracks is completed, RRO correction information unique to all the tracks is obtained. The RRO correction information for each track for which learning has been completed is stored in a semiconductor memory or the like so that it can be used immediately when necessary.

  Here, in the case of an apparatus that performs tracking servo control for on-tracking the magnetic head 23 by VCM control, the VCM 25 is controlled by the MPU 32 and the SVC 34. However, the RRO correction information is transferred from the SVC 34 to the actual VCM 25. It is added to the instruction value for outputting the voltage after conversion into the same control format within the MPU 32. As a learning method of RRO correction information here, a method called RRO correction of repetitive control using DFT (discrete Fourier transform) or adaptive feedforward correction is used.

  From this state, a method for measuring the offset correction value used in the offset correction method of the present invention suitable for DTM / BPM will be described below.

  In the conventional offset measurement, the offset between the read core 23R and the write core 23W has been treated as determined by the yaw angle of the magnetic head 23 and the specifications of the magnetic head 23 itself. That is, since the yaw angle also changes unambiguously simultaneously with the on-track position (radial position) changed by the rotary actuator, the offset between the read core 23R and the write core 23W is the offset unique to the magnetic head (the first offset). It has been treated as the only value that is determined for each track by adding the change caused by the yaw angle position (the cause of the second offset). However, in a high track density environment or an environment with a large positional information distortion such as DTM / BPM, it is not accurate unless the third element of servo information distortion (the cause of occurrence of the third offset) is taken into the offset correction value. It is in a situation that cannot be measured.

  The distortion of the servo information that is the cause of the offset between the third read core 23R and the write core 23W is a portion corresponding to a scale that serves as a reference for determining position information based on the radial position of each servo area. It is distortion. This is the third distortion that needs to be taken into account when measuring the offset correction value. As already described in the description of the servo area in relation to FIGS. 19, 20, 21, 23, and 24, the position information of the DTM or BPM created by the ultra-low speed rotation, that is, the track The track spacing is not the same. Therefore, in this embodiment, when the offset correction value is measured, the offset correction value is measured in a state in which each servo area is independently matched to the ruler existing at the position, not the average for one track circumference. .

  The cause of the offset between the first read core 23R and the write core 23W is an offset inherent to the magnetic head 23, and is due to the fact that the formation positions of the read core 23R and the write core 23W are different from the beginning. The cause of the offset between the second read core 23R and the write core 23W is the difference in the apparent position between the read core 23R and the write core 23W due to the yaw angle of the magnetic head 23 determined by the on-track position (radial position) of the rotary actuator. Is due to. The first offset and the second offset are corrected with a temporary offset correction value. That is, since the result of adding the first offset and the second offset corresponds to the offset of the read core 23R and the write core 23W, for example, a temporary offset measurement is performed at the position of the track No. 4 and the average for one track round is performed. If the offset correction value is measured, the value becomes the offset correction value of the read core 23R and the write core 23. Furthermore, when the read core 23R and the write core 23W are positioned on the same target track having a large eccentricity, the yaw angle of the magnetic head 23 changes depending on the rotational position by tracing the track trajectory by the magnetic head 23. In order to correct this, correction as shown in Patent Document 7 is necessary.

  Therefore, in the next step (4), the lead core 23R is offset by the temporary offset correction value, and RRO control is performed in which RRO correction information is not learned based on the RRO correction information before the offset.

(4) Preparatory stage of offset correction value calculation FIG. 26 shows an offset from track No. 4 in the outer direction by two tracks, which are temporary offset correction values of the average read core 23R and write core 23W actually measured in FIG. The state where the lead core 23R is positioned on the track orbit of the track No. 2 is shown. As the RRO correction information at this time, the RRO correction information of the track No. 4 that has been learned and stored in advance with the read core 23R being on-track in the track No. 4 is used as it is. RRO control in a state where no update is performed is performed. That is, FIG. 26 shows the lead core 23R in the outer direction by a distance of 2 tracks corresponding to a temporary offset correction value while performing RRO control without updating RRO correction information with the RRO correction information of track No. 4. The ideal state when moved to is shown.

  However, if the magnetic head 23 is moved two tracks in the outer direction, the magnetic head 23 (read core 23R) moves from the vicinity of the track No. 4 where the track was initially on-track to the vicinity of the track No. 2, so that it can be detected. The state of distortion is different. When the RRO control based on the RRO correction information learned in step (3) is executed on the position signal detected by the lead core 23R due to the change in distortion, the state shown in FIG. 26 cannot be maintained, and the position signal shown in FIG. The on-track trajectory of the light core 23W changes to such a shape. As a result, the track No. 4 cannot be accurately traced by the write core 23W, and the write core 23W cannot be positioned at an accurate position.

  Therefore, in order to accurately position the write core 23W on the target track in the next step (5), the RRO learned by positioning the read core 23R in step (3) in a state where the read core 23R is corrected with the temporary offset correction value. While performing the RRO control based on the correction information in step (4), the position control is performed using the offset value at which the position error becomes zero in step (5). The offset value at which this position error becomes zero is the offset correction value to be obtained.

(5) Stage of accurately positioning the write core 23W on the target track FIG. 28 shows the positioning of the read core 23R on the track No. 4 in step (3) in order to accurately position the write core 23W on the target track No. 4. Position error in a state where the lead core 23R is corrected with a temporary offset correction value while the RRO control is performed using the learned RRO correction information (a position where the lead core 23R is offset from the state where the lead core 23R is positioned on the track No. 4 by two tracks in the outer direction). This shows a state when position control is performed using an offset value that becomes zero. As a result of performing position control using the offset correction value at which the position error becomes zero, the track trajectory of the lead core 23R approaches the trajectory when positioned at track No. 4, and the VCM drive current or VCM drive voltage applied to the VCM 25 However, the VCM drive current or the VCM drive voltage having the same waveform is applied to the VCM 25 at the same timing as when the read core 23R is on-tracked to the track No. 4.

  The position control performed using the offset value at which the position error is zero here means that the servo is performed while performing the RRO control based on the RRO correction information measured in advance without performing the learning update of the RRO correction information. This is control in which information is demodulated and correction is performed so that RRO (standing wave position error) generated when the position information is used for position control becomes zero. That is, when the read core 23R and the write core 23W are accurately positioned on the same target track for one track, the read core is excluding the deviation due to the different yaw angles generated when the read core 23R and the write core 23W are positioned. This position control focuses on the fact that the VCM drive current or VCM drive voltage for controlling 23R and the write core 23W must be the same. In other words, if the same RRO correction information is used for a track whose trajectory is different from the original track trajectory for which the RRO correction information is measured, no positional error occurs in the original track, but RRO correction information for a different track trajectory is used. In the track (the state where the write core 23W is positioned at the track No. 4), the RRO due to the position error occurs due to the difference in the originally required RRO correction information. Therefore, by adding a correction for making RRO to zero in a state where the write core 23W is positioned on the track No. 4, the track trajectories of the read core 23R and the write core 23W to be traced are made substantially the same. Made it possible.

  In other words, the VCM drive current or VCM drive voltage applied to the VCM 25 for tracing the track trajectory must be able to trace the target track trajectory only by this VCM drive current or VCM drive voltage. However, in the current HDD where the track density is high and the track pitch is narrow, the track trajectory cannot be accurately traced only with this VCM drive current or VCM drive voltage, and a position error occurs in the form of RRO. Normally, this RRO is dealt with by tracing by RRO tracking control. Therefore, when tracing the trajectory of the target track accurately, the sum of the current or voltage determined by the RRO tracking control and the current or voltage determined from the position error information of the servo signal is used as the VCM drive current or VCM drive voltage. Adding to the VCM 25 enables accurate tracing.

  Here, the RRO correction information of the track No. 4 determined from the RRO correction information accurately learned when the lead core 23R is positioned at the track No. 4 and the track of the track No. 4 is traced is defined as An. The RRO position error value of track No. 4 determined from position error information that could not be learned other than correction information is defined as Bn. Since the RRO position error value Bn at this time is immediately after the completion of the RRO correction of the track No. 4 accurately, it can be considered that the RRO position error is almost zero, and can be substantially defined as Bn = 0. . The variables An and Bn used here and the variables Cn, Dn, 4Rn, 4Wn, RHn, WHn, and Zn used in the future correspond to each servo sector existing on the magnetic disk. A value for identifying the servo sector number is substituted. For example, when there are 200 servo sectors, a number from 1 to 200 for identifying the servo sector number is substituted for n.

  Next, when the write core 23W is positioned on the track No. 4, the position information used for the actual position control is near the track No. 2 as a result of the temporary offset measurement. The trajectory near 2 will be traced. The position control at this time is performed while performing the RRO control using the RRO correction information An accurately learned when the read core 23R is positioned at the track No. 4. Therefore, the RRO control value here is the same as the RRO control value of track No. 4. Further, the RRO position error value Cn determined from the position error information when tracing the trajectory near the track No. 2 is the RRO correction information when the true RRO near the track No. 4 and the track No. 2 are the same. Are the same An, and the RRO control value applied in the RRO follow-up control is also the same. Therefore, the position error is almost zero, and Cn = 0 should be substantially obtained. However, in DTM and BPM, due to the manufacturing problems already described, the position signal that is a reference for providing accurate position information is distorted, and the generated RRO has a different shape depending on the track to be positioned.

  Specifically, when the RRO control using the RRO correction information An that is accurately learned when the read core 23R is positioned near the track No. 2 and the read core 23R is positioned at the track No. 4 is performed. Therefore, the VCM drive current or the VCM drive voltage based on the RRO control value is applied to the VCM 25. Next, since the temporary offset correction value is −2 tracks, the read core 23R is positioned near track No. 2 and position control is performed so as to trace the track of track No. 2. However, the RRO control using the RRO correction information An originally learned in the track No. 2 is performed here using the RRO correction information An of the track No. 4. For this reason, the VCM 25 is forcibly driven by the RRO control using the RRO of the track No. 2 and the RRO correction information An of the track No. 4 due to the fact that the RRO of the track No. 2 remains without being corrected. A VCM drive current or a VCM drive voltage that generates an RRO position error value Cn of the position error caused by the combined RRO of the two RROs with the RRO of the cause is added to the VCM 25. That is, when the lead core 23R is positioned at the track No. 2 and the track is traced, the VCM 25 generates the VCM drive current or the VCM drive voltage and the RRO position error value Cn based on the RRO correction information An. The current or VCM drive voltage is added and applied simultaneously.

  The condition for the read core 23R and the write core 23W to trace the same track trajectory is that the VCM drive current or VCM drive voltage to be applied to the VCM 25 is when the read core 23R is positioned in the track No. 4 and the write core 23W in the track No. 4 Therefore, the RRO position error value Cn needs to be made close to zero because it is necessary to calculate the RRO control value based on the RRO correction information An of the same track No. 4 at the time of positioning. The actual RRO position error value Cn is the RRO position error generated as a result of performing tracking servo control while performing RRO control with the RRO correction information An for the position information including the third distortion of the track No. 2 Value. Therefore, it is necessary to introduce the correction value Dn of the position information so that the RRO position error value Cn becomes zero and correct the position information input to the servo tracking control. The position information correction value Dn needs to be selected so that the RRO position error value Cn as a result of executing the trace of the track No. 2 while performing the RRO control with the RRO correction information An approaches zero. The correction value Dn corresponds to the difference between the temporary offset correction value (average value of one round of the target track) and the true offset correction value of each servo sector.

  In order to bring the RRO position error value Cn close to zero, it is only necessary that the trajectory in the absolute space after the offset correction of the track No. 2 has the same shape (similar shape) as the track No. 4. That is, the VCM drive current or the VCM drive voltage applied to the VCM 25 for positioning each track and tracing the track is the same as that calculated from the RRO control value based on the RRO correction information An. Means that. That is, position information obtained by demodulating track No. 2 while performing RRO control using the RRO correction information An learned when positioning the read core 23R on track No. 2 and positioning the read core 23R on track No. 4 When the tracking servo control is performed on the result of adding the correction value Dn to the RRO position error value Cn for the track No. 4 of the write core 23W becomes almost zero. In other words, the position control is performed on the result of adding the correction value Dn of each servo sector to the position information when the read core 23R is positioned on the track No. 2, and the track No. 2 is used for the RRO correction of the track No. 2. By performing the RRO control using the RRO correction information An of 4, the VCM drive current or the VCM drive voltage applied to the VCM 25 is unlimited, and the RRO control is performed with the RRO correction information An when the read core 23R is positioned on the track No. 4. This is the same as the VCM drive current or VCM drive voltage applied to the VCM 25 when performing. As a result, the light core 23W can trace the track No. 4 accurately.

“Correction value Dn: Offset correction value”
A specific method for calculating the correction value Dn is as follows. The RRO position error value Cn is converted from the time domain to the frequency domain by DFT (Discrete Fourier transform), and the RRO position error value Cn in the frequency domain is tracked with the compression characteristics used in the tracking servo control at this time. It is obtained by converting the position information input to the servo control and converting the result into the original time domain. That is, the correction value Dn obtained here is such a correction value that the RRO position error value Cn becomes zero when the read core 23R is positioned on the track No. 2 and the RRO control is performed with the RRO correction information An. This corresponds to the third offset value in servo sectors existing between the write core 23W and the write core 23W.

  Further, the offset correction value can be calculated by adding the correction value Dn, which is the third offset value, and the temporary offset value corresponding to the first and second offset values. RRO control using the RRO correction information of the target track in addition to the offset correction value for each servo sample (read servo area SA and position information demodulation) for each servo sample obtained here. As a result, the light core 23W is positioned on the target track. Incidentally, the lead core 23R can be positioned on the target track by performing RRO control using the RRO correction information of the target track without adding the offset correction value to the read position information.

  The series of processing of steps (1) to (5) described above with reference to FIGS. 24 to 28 is performed on all tracks, so that the read core 23R and the write core can be written without writing formal offset measurement data. 23W offset correction value can be measured. In short, the temporary offset measurement data is written only in the first place (once per track), the average of the offset correction values of the track is obtained, and the average value is extended to the adjacent track and shifted. In this case, the offset correction value for the entire track can be detected in a relatively short time even on a magnetic disk medium such as DTM / BPM by performing correction each time. The correction is performed every time the average value of the offset correction values measured with the temporary offset measurement data in steps (1) and (2) is corrected each time a new track is moved. For example, it is measured in advance every other track or every few tracks (for example, every 100 tracks), and is corrected by interpolation.

  In the above embodiment, the RRO correction information of the track No. 4 is learned again after the temporary offset correction value is measured. However, the information is learned at the same time while the temporary offset correction value is being written and the result is stored. You may keep it.

  The VCM drive current or VCM drive voltage for on-track control of track No. 4 and the VCM drive current or VCM drive voltage for on-track control of track No. 2 shown in the above description of the embodiment are almost the same. The method and means for doing this are merely examples, and if the VCM drive current or VCM drive voltage for track No. 4 and the VCM drive current or VCM drive voltage for track No. 2 can be made substantially the same as the object of the present invention, Any method or means may be used. Here, when the track No. 4 VCM drive current or VCM drive voltage and the track No. 2 VCM drive current or VCM drive voltage are almost the same, the track trajectories of the read core 23R and the write core 23W write or read data. If it is within a range that does not interfere with the recording, or if the condition that the data in the center track is not erased when data is written to both tracks at the same time is satisfied on the entire surface of the magnetic disk , Means not necessarily the same.

(6) Storage of offset correction value and RRO correction information Finally, the offset correction value and RRO correction information for which the measured position error for positioning the write core 23W used here at the center of the target track becomes zero is a semiconductor It is stored in an independent storage area such as a memory (position correction information storage area 38 of the flash ROM 33) or written in a predetermined area of the magnetic disk medium. Thus, before the writing operation is performed, an offset correction value and RRO correction information that makes the position error of the target track become zero are read and prepared in advance for one round of the track. If servo area measurement decimation and track measurement decimation are performed, the necessary offset correction values and RRO correction information are calculated in advance by interpolation or copying at the stage of storing the offset correction values. Remember.

  Thus, before the data writing process is performed on the target track of the magnetic disk medium, the offset correction value and the RRO correction information of the target track are written only for the track necessary for the control of the target sector to be written, or the entire track. The correction information necessary for controlling the sector in the middle of reaching the target sector and the target sector is read in advance by one of the following one sector in advance, one by one in advance.

“Example 2 of offset correction value measurement using RRO tracking control”
Also in the second embodiment of offset correction value measurement using RRO tracking control, processing equivalent to writing and reading of temporary offset measurement data is the same as steps (1) and (2) described with reference to FIG. Write and read. Accordingly, the second method of measuring the offset correction value using the RRO follow-up control of the present invention from the formal offset measurement data writing process after the end of steps (1) and (2) will be further described with reference to FIGS. This will be described with reference to FIG.

(3-2) RRO correction information learning stage 2
FIG. 29 shows a point in time when the learning stage of the RRO correction information (first RRO correction information) of the track whose formal offset correction value is measured is completed. In this figure, in order to measure the offset correction value of track No. 4, the read core 23R is on-tracked to track No. 4 and RRO correction information 4Rn (first RRO correction information) is learned, and the end point is shown. ing.

FIG. 30 shows that the magnetic head 23 is moved in the outer direction by two tracks corresponding to the provisional offset correction value from the track No. 4 where the official offset correction value is measured, and the lead core 23R is further moved to this position, that is, near the track No. 2. The RRO correction information 4Wn (second RRO correction information) is learned by turning on the track, and the time point when it is finished is shown.
The learning of the first RRO correction information 4Rn and the second RRO correction information 4Wn is performed by the same method as step (3) in the first embodiment. In this embodiment, the integers of the sign portions of the first RRO correction information 4Rn and the second RRO correction information 4Wn, and 4 in this embodiment, indicate the track number for measuring the official offset correction value.

  The offset correction value measurement method 2 used in the offset correction method of the present invention will be described below from the state in which the learning of the first RRO correction information 4Rn and the second RRO correction information 4Wn is completed. Furthermore, here, a method for measuring an offset correction value corresponding to the third distortion while performing RRO control without learning RRO correction information will be described.

(4-2) Preparatory stage 2 for calculating the offset correction value
In the state where learning of the RRO correction information when the lead core 23R is positioned on each of the track No. 4 and the track No. 2, the learning of the RRO correction information 4Rn and 4Wn from the learned RRO correction information 4Rn and the track No. 4 is performed. The actual trajectory of the lead core 23R when positioned as No. 2 is estimated by calculation. The track trajectory calculated at this time indicates the transition position from the average position of track No. 4 and track No. 2 for each servo sample, that is, the transition position for each servo sample from each track center TrC.

  In the tracking servo control, when the RRO correction information is given as an operation amount to the plant as a VCM drive current or a VCM drive voltage, a change corresponding to the operation amount occurs in the VCM 25. That is, when the RRO correction information is given to the VCM 25, a fluctuation corresponding to the RRO correction information occurs in the VCM 25. As a result, the position of the magnetic head 23 at the tip of the VCM 25 also changes in proportion. Since this can be regarded as a shift amount in an absolute space, in other words, a shift amount from an ideal circular orbit, from the two first RRO correction information 4Rn and the second RRO correction information 4Wn, each shift amount RHn ( The first displacement amount) and the displacement amount WHn (second displacement amount) can also be calculated. In this embodiment, the plant starts from the part that receives the instruction value (digital value in the case of digital servo) output from the MPU 32 until the result is output and passed to the MPU 32. Therefore, in this embodiment, the SVC 34, the magnetic head 23, the carriage arm 24, and the VCM 25 correspond to a plant.

  A specific method for calculating the displacements RHn and WHn of the magnetic head 23 is as follows. The first shift amount RHn and the second displacement amount WHn are obtained by converting the first RRO correction information 4Rn and the second RRO correction information 4Wn from the time domain to the frequency domain by DFT, and for the plant used in the tracking servo control at this time. By converting the first RRO correction information 4Rn and the second RRO correction information 4Wn converted to the frequency domain with the response characteristics of the frequency domain, the first shift amount based on the first RRO correction information 4Rn output from the plant It is obtained by converting the RHn and the second RRO correction information 4Wn into the frequency domain value of the second transition amount WHn and converting the result into the original time domain. That is, the value of the time domain obtained here is the first change amount RHn of each magnetic head 23 when the read core 23R is positioned on the track No. 4 and when the read core 23R is positioned on the track No. 2. And the second transition amount WHn. The difference between the first displacement amount RHn and the second displacement amount WHn is the third offset value for each servo sector existing between the read core 23R and the write core 23W (equivalent to when the read core 23R is positioned at track No. 2). It corresponds to. As the frequency response characteristics of the plant used here and the frequency response characteristics of the plant model described above, it is desirable to actually measure and use the frequency response characteristics of the actual controlled object.

(5-2) Stage 2 of accurately positioning the write core 23W on the target track
First, the difference RHn−WHn is calculated from the first transition amount RHn and the second transition amount WHn calculated when the read core 23R is positioned on track No. 4 and track No. 2 calculated in step (4-2). Thus, the track deviation Zn corresponding to the track deviation in the absolute space of the track No. 4 and the track No. 2 is calculated. The orbital deviation Zn calculated here was subjected to RRO control with the RRO correction information An learned and stored when the lead core 23R was positioned on the track No. 2 and the lead core 23R was positioned on the track No. 4. It becomes almost the same value as the RRO position error value Cn that occurs sometimes. The RRO position error value Cn is different from the RRO position because the RRO control using the RRO correction information 4Wn of the track No. 2 is performed when the second displacement amount WHn used in the calculation of the orbital deviation Zn is measured. This is a part where the measurement trajectory is different from that when measuring the error value Cn. Therefore, although it does not completely coincide with the RRO position error value Cn described in the first embodiment of the present invention, the orbital deviation Zn can be used as long as the error can be tolerated.

  Next, in order to position the write core 23W on the track No. 4, the read core 23R is controlled while performing the RRO control with the first RRO correction information 4Rn learned and stored when the read core 23R is positioned on the track No. 4. A correction value Dn that is positioned on the track No. 2 and generates a trajectory deviation having a reverse characteristic of the trajectory deviation Zn is calculated from the trajectory deviation Zn. This regards the orbital deviation Zn as the RRO position error value Cn, calculates the correction value Dn by the same method as in the first embodiment of the invention, and positions the lead core 23R on the track No. 2 using the result as the correction value of the position information. This is realized by adding the position information read out sometimes. FIG. 31 shows the RRO using the first RRO correction information 4Rn learned and stored when the read core 23R is positioned on the track No. 4 in order to accurately position the write core 23W on the target track No. 4. This shows a state in which tracking servo control is performed on the result of adding the correction value Dn to the position information obtained by demodulating track No. 2 while performing control. Therefore, the write core 23W is in a state where the track No. 4 is accurately traced. That is, the correction value Dn obtained here is an offset correction value that makes the position error zero, and is an offset correction value that corrects the third offset existing between the read core 23R and the write core 23W in units of servo sectors. .

  Further, the offset correction value can be calculated by adding the correction value Dn, which is the third offset value, and the temporary offset value corresponding to the first and second offset values. RRO control using the RRO correction information of the target track in addition to the offset correction value for each servo sample (read servo area SA and position information demodulation) for each servo sample obtained here. As a result, the light core 23W is positioned on the target track. Incidentally, the lead core 23R can be positioned on the target track by performing RRO control using the RRO correction information of the target track without adding the offset correction value to the read position information.

  By performing the series of processes of steps (1), (2), (3-2), (4-2), and (5-2) described above with reference to FIGS. Measurement of offset correction values of the read core 23R and the write core 23W is possible without writing measurement data. In short, the temporary offset measurement data is written only in the first place (once per track), the average of the offset correction values of the track is obtained, and the average value is extended to the adjacent track and shifted. In this case, the offset correction value for the entire track can be detected in a relatively short time even on a magnetic disk medium such as DTM / BPM by performing correction each time. The correction every time means that the average value of the offset correction values measured with the temporary offset measurement data in steps (1) and (2) is corrected each time a new track is moved. For example, measurement is performed in advance every other track or every several tracks (for example, every 100 tracks), and is corrected by interpolation.

  In the above description, the RRO correction information for track No. 4 and track No. 2 is learned anew after measuring the temporary offset correction value. However, it is learned simultaneously while the temporary offset correction value is being written. The result may be stored. That is, learning in step (3-2) may be executed while step (1) is being executed.

  The method for detecting the track trajectory causing the RRO of the track No. 4 and the track trajectory causing the RRO of the track No. 2 shown in the above description is only one means. Any method may be used to detect the track trajectories of No. 4 and No. 2, and the offset correction values of the read core 23R and the write core 23W based on the detected track trajectories can assure HDD operation. It may be obtained with the accuracy of

  The accuracy within the range in which the operation of the HDD can be assured here may be such that the track trajectories of the read core 23R and the write core 23W may be different within a range that does not hinder the writing and reading of data. This means that it is not necessarily the same as long as the condition that the data in the middle track is not erased when the data is written is within the range of the entire surface of the magnetic disk.

(6-2) Storage 2 of offset correction value and RRO correction information
Finally, the offset correction value and the RRO correction information so that the measured position error for positioning the write core 23W used here at the center of the target track becomes zero are stored in an independent storage area (flash ROM 33) such as a semiconductor memory. In the position correction information storage area 38) or written in a predetermined area of the magnetic disk medium. Thus, before the writing operation is performed, an offset correction value and RRO correction information that makes the position error of the target track become zero are read and prepared in advance for one round of the track. If servo area measurement decimation and track measurement decimation are performed, the necessary offset correction values and RRO correction information are calculated in advance by interpolation or copying at the stage of storing the offset correction values. Remember.

  Thus, before the data writing process is performed on the target track of the magnetic disk medium, the offset correction value and the RRO correction information of the target track are written for only one track or the sector necessary for controlling the target sector to be written. The correction information necessary for controlling the sector in the middle of reaching the target sector and the target sector is read in advance by one of the following one sector in advance, one by one in advance.

  In the first and second embodiments described so far, the case where the track position determined first is the read core 23R is described. However, even when the track position determined first is the write core 23W, the correction direction This can be realized by reversing all of the above and switching the reference of the read core 23R and the write core 23W.

  As described above, in a recording medium having a high track density and an apparatus equipped with DTM / BPM, position information that is not similar is formed on the magnetic disk medium, so that the read core and write corresponding to each piece of position information are written. By having the core offset information independently corresponding to all or all necessary track centers TrC, the write core center can be positioned at the position of the lead core center, and the data is accurately positioned. I can write. The position information in this case may be position information formed in the radial servo area, and may be partially discontinuous. Further, the position information of the radial servo area can be applied to the present invention as long as the tracks for one rotation are grouped even if the tracks are concentric or spiral, which are not similar.

  Embodiments relating to servo patterns formed in the servo area of the magnetic disk medium to which the present invention is applied and their outputs will be described below with reference to FIGS.

“Example 1 of offset measurement data read output by servo pattern”
FIG. 34 shows Example 1 of a NULL servo pattern and offset measurement data read output. This NULL servo pattern is a modified type of the 4-burst servo pattern. In the case of using the 4-burst servo pattern, after reading out burst A and burst B respectively, the MPU 32 calculates the output level difference between bursts A and B. Since A-B (the black and white of the pattern indicates the south and north poles of the magnet) is executed at the time when the servo signal is demodulated, the MPU 32 does not need to perform an operation for obtaining a difference. Since position information can be accurately detected even with this pattern, the above-described four burst servo patterns can all be replaced with NULL servo patterns.

"Example 2 of offset measurement data read output by servo pattern"
FIG. 35 shows a second example of the phase servo pattern and offset measurement data read output. This phase servo pattern is a servo pattern of a different type from the 4-burst servo pattern and the NULL servo pattern. The phase servo pattern detects a phase change by converting it into position information. Since position information can be accurately detected even with this pattern, all of the four burst servo patterns can be replaced with phase servo patterns.

  The present invention is applied to a high-track density magnetic disk device using a magnetic disk medium and a magnetic disk device using DTM / BPM as a magnetic disk medium.

10 Hard disk drive (HDD)
11 Disk enclosure (DE)
12 Circuit board (PCA)
21 Magnetic disk (DISK) (magnetic medium, magnetic medium, disk-shaped recording medium)
21a Magnetic disk surface 22 Spindle motor (SPM)
23 Magnetic head ((HEAD (MR head, TMR head))
23R Lead core 23W Write core 24 Carriage arm 25 Voice coil motor (VCM)
26 Preamplifier 31 Read channel (RDC)
32 MPU
33 Flash ROM (semiconductor memory)
34 Servo Controller (SVC)
35 Hard disk controller (HDC)
36 RAM
37 Interface connector 38 Position correction information storage area 200 201 Ideal circular track 202 203 Actual track 206 207 RRO following track 208 209 ZAP control track 210 211 Actual track trajectory (solid line)
210 211 Ideal track trajectory (dotted line)
300 301 Servo area TrB Track boundary TrC Track center TrCa Ideal track center TrCb Actual track center SA Servo area (position information area)
DA data area

Claims (22)

A plurality of tracks formed around the same center of rotation, or a plurality of tracks separated by a nonmagnetic area, and each track that intersects each track and extends in the radial direction is divided into a plurality of sectors. In order to read or write data with a magnetic head in which a read core and a write core are separately formed on a track of a magnetic disk medium having a plurality of position information areas in the circumferential direction, all or necessary position information areas are An offset correction value measurement method that has an offset correction value of the read core and write core for a corresponding sector, on the premise that the track position of the read core is determined first,
Writing temporary offset measurement data by the write core while reading the position information from the position information area by the read core and performing on-track control for all or necessary tracks corresponding to the position information area;
Reading the temporary offset measurement data from the track by the read core, detecting a radial position where the output level of the read data is a maximum value, and setting a temporary offset correction value;
For the track to be measured, positioning the lead core at the track center and learning RRO correction information while performing RRO tracking control;
Offsetting the lead core from the track to be measured by the temporary offset correction value and executing RRO control according to the learned RRO correction information;
And calculating an offset correction value at which the RRO position error value becomes zero in a state where the write core is corrected with a temporary offset correction value while performing the RRO control. Correction value measurement method. 2. The method of measuring an offset correction value of a magnetic disk apparatus according to claim 1, further comprising measuring an RRO position error value while tracking servo controlling the offset correction value, and converting the RRO position error value from a time domain to a frequency domain by Fourier transform. The RRO position error value in the frequency domain is converted into the position information input to the tracking servo control with the compression characteristics used in the tracking servo control at this time, and the result is converted into the original time domain. And calculating a correction value, and adding the correction value to the temporary offset correction value to obtain an offset correction value measurement method for a magnetic disk device. A plurality of tracks formed around the same center of rotation, or a plurality of tracks separated by a nonmagnetic area, and each track that intersects each track and extends in the radial direction is divided into a plurality of sectors. In order to read or write data with a magnetic head in which a read core and a write core are separately formed on a track of a magnetic disk medium having a plurality of position information areas in the circumferential direction, all or necessary position information areas are An offset correction value measurement method that has an offset correction value of the read core and write core for a corresponding sector, on the premise that the track position of the read core is determined first,
Writing temporary offset measurement data by the write core while reading the position information from the position information area by the read core and performing on-track control for all or necessary tracks corresponding to the position information area;
Reading the temporary offset measurement data from the track by the read core, detecting a radial position where the output level of the read data is a maximum value, and setting a temporary offset correction value;
Learning the first RRO correction information while positioning the lead core at the track center and performing RRO tracking control for the track to be measured;
Learning the second RRO correction information while performing RRO tracking control by offsetting the lead core from the track where the first RRO correction information is learned by the temporary offset correction value;
The track trajectory when the light core was positioned on each track was calculated from the two first and second RRO correction information of each learned track and the offset track, and the calculated track trajectory was measured. Calculating first and second displacement amounts from the average positions of the track and the offset track, respectively;
Calculating the orbital deviation in the absolute space of the target track and the offset track from the difference between the first and second displacement amounts when positioning the light core on the target track;
Offsetting the lead core from the target track by the provisional offset correction value and performing RRO control according to the learned first RRO correction information;
Calculating an offset correction value for generating a trajectory deviation having a reverse characteristic of the trajectory deviation from the trajectory deviation in a state where the light core is corrected with a temporary offset correction value while performing the RRO control. A method of measuring an offset correction value of a magnetic disk device, characterized in that: 4. The method of measuring an offset correction value for a magnetic disk device according to claim 1, wherein the step of learning the RRO correction information by positioning the read core on a target track is the step of writing the temporary offset correction value. A method of measuring an offset correction value of a magnetic disk device, executed while writing an offset correction value. 4. The method of measuring an offset correction value for a magnetic disk apparatus according to claim 3, wherein the first and second shift amounts are converted from the time domain to the frequency domain by Fourier transform from the first and second RRO correction information. A method for measuring an offset correction value of a magnetic disk device, comprising: converting a value output from a plant with a response characteristic in a frequency domain of a tracking servo control target plant and converting the result into an original time domain. 4. The offset correction value measuring method for a magnetic disk device according to claim 3, wherein the offset correction value is further used for tracking servo control at this time by converting the orbital deviation from a time domain to a frequency domain by Fourier transform. The trajectory deviation in the frequency domain is converted into position information at the time of input to the tracking servo control by the compression characteristic, the result is converted to the original time domain, a correction value is calculated, and the temporary offset correction value is obtained. A method for measuring an offset correction value of a magnetic disk apparatus, comprising the step of adding the correction values to obtain the correction value. A plurality of tracks formed around the same center of rotation, or a plurality of tracks separated by a nonmagnetic area, and each track that intersects each track and extends in the radial direction is divided into a plurality of sectors. In order to read or write data with a magnetic head in which a read core and a write core are separately formed on a track of a magnetic disk medium having a plurality of position information areas in the circumferential direction, all or necessary position information areas are An offset correction value measuring method for providing an offset correction value of the read core and write core for a corresponding sector, on the premise that the track position of the write core is determined first,
Writing temporary offset measurement data by the write core while reading the position information from the position information area by the read core and performing on-track control for all or necessary tracks corresponding to the position information area;
Reading the provisional offset measurement data from the track by the read core, detecting a radial position where the output level of the read data is a maximum value, and measuring a provisional offset correction value;
For the track to be measured, positioning the lead core at the track center and learning RRO correction information while performing RRO tracking control;
The read core is read in the temporary offset correction value measurement and moved to a radial position where the output level of the read data becomes the maximum value, and RRO control is performed according to the learned RRO correction information. Performing the steps,
Calculating an offset correction value at which the RRO position error value becomes zero in a state where the lead core is corrected with a temporary offset correction value while performing the RRO control. Value measurement method. 7. The method of measuring an offset correction value of a magnetic disk apparatus according to claim 6, further comprising measuring an RRO position error value while tracking servo controlling the offset correction value, and converting the RRO position error value from a time domain to a frequency domain by Fourier transform. The RRO position error value in the frequency domain is converted into the position information input to the tracking servo control with the compression characteristics used in the tracking servo control at this time, and the result is converted into the original time domain. And calculating a correction value, and adding the correction value to the temporary offset correction value to obtain an offset correction value measurement method for a magnetic disk device. A plurality of tracks formed around the same center of rotation, or a plurality of tracks separated by a nonmagnetic area, and each track that intersects each track and extends in the radial direction is divided into a plurality of sectors. In order to read or write data with a magnetic head in which a read core and a write core are separately formed on a track of a magnetic disk medium having a plurality of position information areas in the circumferential direction, all or necessary position information areas are An offset correction value measuring method for providing an offset correction value of the read core and write core for a corresponding sector, on the premise that the track position of the write core is determined first,
Writing temporary offset measurement data by the write core while reading the position information from the position information area by the read core and performing on-track control for all or necessary tracks corresponding to the position information area;
Reading the temporary offset measurement data from the track by the read core, detecting a radial position where the output level of the read data is a maximum value, and setting a temporary offset correction value;
Learning the first RRO correction information while positioning the lead core at the track center and performing RRO tracking control for the track to be measured;
The read core is moved from the track having learned the first RRO correction information to the radial position where the temporary offset measurement data is read out by the temporary offset correction value measurement and the output level of the read data becomes the maximum value. Learning the second RRO correction information while performing RRO tracking control;
The track trajectory when the light core was positioned on each track was calculated from the two first and second RRO correction information of each learned track and the offset track, and the calculated track trajectory was measured. Calculating first and second displacement amounts from the average positions of the track and the offset track, respectively;
When the light core is positioned on the target track, the RRO position error value is calculated by calculating the trajectory deviation in the absolute space of the target track and the offset track from the difference between the first and second displacement amounts. Stages,
Offsetting the lead core from the target track by the provisional offset correction value and performing RRO control according to the learned first RRO correction information;
Calculating an offset correction value for generating a trajectory deviation having a reverse characteristic of the trajectory deviation from the trajectory deviation in a state where the light core is corrected with a temporary offset correction value while performing the RRO control. A method of measuring an offset correction value of a magnetic disk device, characterized in that: 10. The method of measuring an offset correction value for a magnetic disk device according to claim 7, wherein the step of learning the RRO correction information by positioning the read core on a target track is the step of writing the temporary offset correction value. A method of measuring an offset correction value of a magnetic disk device, executed while writing an offset correction value. 10. The method of measuring an offset correction value of a magnetic disk device according to claim 9, wherein the first and second shift amounts are converted from the first and second RRO correction information from time domain to frequency domain by Fourier transform. A method for measuring an offset correction value of a magnetic disk device, comprising: converting a value output from a plant with a response characteristic in a frequency domain of a tracking servo control target plant and converting the result into an original time domain. 10. The method of measuring an offset correction value of a magnetic disk device according to claim 9, wherein the offset correction value is used for tracking servo control at this time by converting the orbital deviation from a time domain to a frequency domain by Fourier transform. The trajectory deviation in the frequency domain is converted into position information at the time of input to the tracking servo control by the compression characteristic, the result is converted to the original time domain, a correction value is calculated, and the temporary offset correction value is obtained. A method for measuring an offset correction value of a magnetic disk apparatus, comprising the step of adding the correction values to obtain the correction value. 13. The method of measuring an offset correction value of a magnetic disk device according to claim 1, wherein the offset correction value is a single or continuous thinning-out in a sector unit or a track unit and a combination of a sector unit and a track unit. A method of measuring an offset correction value of a magnetic disk device, which is an offset correction value of the read core and the write core with respect to a sector corresponding to the position information area, measured in a state in which 13. The offset correction value method for a magnetic disk device according to claim 1, wherein the RRO control correction information for which learning has been completed is performed when the read core is on-tracked to a learning target track, and A method for measuring an offset correction value of a magnetic disk device, wherein the same value is used as correction information for RRO control when the write core is on-track. 15. The method of measuring an offset correction value of a magnetic disk device according to claim 1, wherein the offset correction value of the sector corresponding to the all or all necessary position information areas and the RRO control are used. A method of measuring an offset correction value of a magnetic disk device, comprising: storing all learned or all necessary correction information in a storage unit of the magnetic disk device in advance. 16. The method of measuring an offset correction value of a magnetic disk device according to claim 15, wherein a necessary offset correction value is calculated in advance from the thinned offset correction value by interpolation or copying and stored in a storage means of the magnetic disk device. An offset correction value measuring method for a magnetic disk device including 17. The method of measuring an offset correction value for a magnetic disk device according to claim 15, wherein the storage means is a semiconductor memory. 17. The method for measuring an offset correction value of a magnetic disk device according to claim 15, wherein the storage means is a specific area of the magnetic disk, and includes a step of writing in the specific area in advance. . 19. An offset correction method for a magnetic disk device comprising storage means for storing offset correction values and correction information according to claim 15, wherein the track position of the read core is determined first. In
When writing to the magnetic disk by the write core, the step of reading the offset correction value corresponding to each target sector to be written and the correction information learned for the RRO control from the storage means in advance, or A method for correcting an offset of a magnetic disk device, comprising: reading from the specific area of the magnetic disk by a read core. A magnetic disk device comprising storage means storing the offset correction value and correction information according to any one of claims 15 to 18, wherein the track position of the read core is determined first.
When writing data to the magnetic disk medium by the magnetic head, the offset correction value corresponding to the target sector and the correction information learned for the RRO control are read from the storage means, and the offset correction control and the RRO control are performed. And
Control means for reading the correction information learned for the RRO control corresponding to the target sector from the storage means and performing the RRO control when reading data from the magnetic disk medium by the magnetic head; A magnetic disk device characterized by the above. 19. A method for correcting an offset of a magnetic disk device comprising storage means for storing offset correction values and correction information according to claim 15, wherein the track position of the write core is determined first. Assuming
When reading from the magnetic disk by the read core, the offset correction value corresponding to each target sector to be read and the correction information learned for the RRO control are read in advance from the storage means, or in advance by the read core A method of correcting an offset of a magnetic disk device, comprising any one of steps of reading from the specific area of the magnetic disk. A magnetic disk device comprising storage means storing the offset correction value and correction information according to any one of claims 15 to 18, wherein the track position of the write core is determined first.
When reading data from the magnetic disk medium by the magnetic head, the offset correction value corresponding to the target sector and the correction information learned for the RRO control are read from the storage means to perform the offset correction control and the RRO control. ,
Control means for reading the correction information learned for the RRO control corresponding to the target sector from the storage means and performing RRO control when data is written to the magnetic disk medium by the magnetic head. A magnetic disk drive characterized by that.

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