|Publication number||USRE40955 E1|
|Application number||US 09/765,891|
|Publication date||Nov 10, 2009|
|Filing date||Jan 18, 2001|
|Priority date||May 1, 1996|
|Also published as||US5867343|
|Publication number||09765891, 765891, US RE40955 E1, US RE40955E1, US-E1-RE40955, USRE40955 E1, USRE40955E1|
|Inventors||Me Van Le, Jong-Ming Lin|
|Original Assignee||Samsung Electronics Co., Ltd.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (7), Referenced by (5), Classifications (6), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present application is an REI of 08/713,872 filed Sep. 13, 1996, now U.S. Pat. No. 5,867,343, which is a continuation-in-part application of U.S. patent Ser. No. 08/641,685, now U.S. Pat. No. 6,008,962, entitled “Method and Apparatus for Providing Read and Write Skew Offset Information for a Magneto-Resistive Head” filed May 1, 1996.
1. Field of the Invention
The present invention relates in general to disk storage systems and more particularly, to a method and apparatus for providing and storing skew offset information for aligning the read element of a magneto-resistive (MR) head with the centerline of written data during a read operation.
2. Description of the Related Art
Disk drives are magnetic recording devices used for the storage of information. The information is recorded on concentric tracks on either surface of one or more magnetic recording disks. The disks are rotatably mounted to a spin motor and information is accessed by means of read/write heads that are mounted to actuator arms which are rotated by a voice coil motor. The voice coil motor is excited with a current to rotate the actuator and move the heads. The read/write heads must be accurately aligned with the storage tracks on the disk to ensure proper reading and writing of information.
To accurately write and read data, it is desirable to maintain the head on the center of the track. To assist in controlling the position of the head, each sector of the disk typically contains a number of servo bits accurately located relative to the centerline of the track. The signals produced by the servo bits are typically demodulated into position offset signals which are used to determine the position of the head relative to the track, and to move the actuator arm if the head is not located on the track centerline.
There has been developed a dual element transducer which includes a single write element and a separate read element which is constructed from a magneto-resistive material. Such dual element transducers are commonly referred to as magneto-resistive (MR) heads. Because of manufacturing tolerances, the separate magneto-resistive read element may be off-center or skewed from the write element of the head. Therefore, if data is written off the center of the track, to read the data, the servo system must move the head slightly off-center so that the read element is centered with the written data.
Additionally, while the head and write elements may be aligned with the head is positioned over a particular track, when the head is moved to another track, the read element may no longer be aligned with the write element. For example, as shown in
It also has been determined that the skew offset information for an MR head located over the inner tracks of a disk is different from that of an MR head located over the outer tracks of a disk. In addition, such MR head skew offset information is typically non-linear, and it also generally varies greatly between heads.
Accordingly, there is a need in the technology for a method and apparatus for providing skew offset information used in the alignment of a magneto resistive head, so that a read element of an MR head may be aligned with the centerline of written data during a read operation.
In non-MR servo systems, the stored parameters are read during a power up sequence so as to optimize the performance for the particular drive. In systems utilizing an MR head, the data written on the dedicated tracks may not be centered exactly on the tracks because the read and write heads are offset. As a result, when the system attempts to read the written data, additional time is required to locate the centerline of written data. Alternatively, several attempts to read the written data may be required before successfully acquiring the written data. To compound this problem, the associated parameters are typically written on the outermost tracks of the disk where the largest offset between the read and write elements generally occurs.
Accordingly, there is also a need in the technology for an apparatus and method of storing system parameters so that hard drive assemblies utilizing MR heads may efficiently retrieve the stored information.
A method and apparatus for storing position offset information not used for aligning the read element of an MR head with the centerline of written data, during a read operation. The skew or offset between the read and the write elements on a read head is first calculated. The offset information then stored on one or more dedicated tracks of the disk. To accomplish this, the write element is aligned with the centerline of the dedicated track. The position offset information is then written in the data field of the dedicated track. During the power-on process, the read element is aligned with the centerline of the dedicated track and the position offset information may be retrieved by simply reading the information previously stored on the dedicated track.
Referring to the drawings more particularly by reference numbers,
The electronic circuit 120 is coupled to one of the magnetic heads 110 which senses the magnetic field of a magnetic disk 102. When reading the servo information located in the servo field region 110 on the disk 102, the head 110 generates a read signal that corresponds to the magnetic field of the disk 102. The read signal is first amplified by the preamplifier 122, and then provided to the R/W channel circuit 124. The AGC data included in the read signal is provided to the R/W AGC and filter circuit 126. The AGC data provided by the read signal is monitored by the R/W AGC circuit portion of circuit 126 and the read signal is then filtered by the filter circuit located in the circuit 126. The fullwave rectifier 128 rectifies the read signal and provides the rectified read signal to the peak detector 130. In response, the peak detector 130 detects the amplitude of the read signal. The read signal is then provided to the ADC 134 which provides digitized samples of the analog read signal. The digitized signal is then provided to a digital signal processor 136 which generates the position offset signals based on the servo information read by the head 110, as discussed in detail in the following sections. The values representing the position offset signals are stored in memory 140. The bursts sequencer and timing circuit 138 provide the timing required for the aforementioned processes.
As shown in
The heads 110 can magnetize and sense the magnetic field of the disk 102. In one embodiment, each head 110 has a single write element 164 and a separate read element 166 as shown in FIG. 5. The read element 166 is preferably constructed from a magneto-resistive material which changes resistance in proportion to the intensity of an external magnetic field. The read element 166 is sometimes off-set from the write element 164 because the tolerances associated with the manufacturing process of the head. Additionally, the center of the read element 166 may be offset from the center of the write element 164 because of the skew angle of the head 110 with respect to the track on the disk 102. If the read element 166 is aligned with the center CL of the track, and the write element 164 is off-set from the read element 166, the data will be written off-center from the center CL of the track. To properly read the data, the read element 164 must be moved over to the off-center location of the written data.
The servo field 158 in each sector contains a number of servo bits designated A, B, C and D. The boundary formed by the A and B servo bits defines a track CL of the disk 102. The center of the C servo bit is aligned with the center CL of the track. The D servo bit is offset 180° from the position of the C servo bit. The servo bits A and B are used to center the read element with the centerline CL of the dedicated track where the value of A-B corresponds to the off-track position of the head 110 if A-B is a non-zero value. This is accomplished by detecting the amplitude of the servo bursts provided by servo bits A, B, C and D using the read element 166 of the head 110. If the center of the read element 166 is not aligned with the center of the write element 164 (and thus, the center of the written data), then the servo controller 132 will generate a position offset signal using the technique of the present invention, to move the head 110 so that alignment of the center of the read element 166 with the center of the written data may be accomplished.
The distance that the head 110 has to be moved in such a situation is determined by the offset between the read element 166 and the write element 164 for a particular track. The technique of the present invention determines the magnitude of this offset through the use of a calibration burst E. The calibration burst E has a centerline located at a predetermined off-set position from the track centerline CL. The centerline of the calibration burst E is also the center of the write element 164 since the calibration bursts E are written by the write element 164 during the calibration process of the disk drive.
Next, the process S180 obtains a profile of the calibration burst E with respect to the center CL of each track by sampling the amplitude of the calibration burst E over the width of the track, as shown in process step S186. This is done by first performing a seek to a position that is −50% from the center of the track, and then micro-jogging the head 110 in increments, from a position that is −50% from the center of the track to a position that is +50% from the center of the track, and reading the amplitude of the calibration burst E. This routine is repeated for all servo sectors in which a calibration burst E has been written.
The position value d corresponding to the peak value of the calibration burst E represents the offset value between the read and write elements 164 and 166, at a particular track location. The position offset signal should be ideally zero when the read element 166 is centered with the written data. If the read element 166 is off-set from the write element 164 the position offset signal has some non-zero value when the read element is centered over the written data.
Upon obtaining the offset value, the servo controller 132 will generate a position offset signal having an amplitude representative of the offset value, as shown in process step S188. The value of the position offset signal corresponding to a particular track and sector is stored in RAM 140 for use during normal operation of the disk drive 100 as shown in process step S190. In one embodiment, the position offset values corresponding to the track number (as identified by gray code) and the ID number (which provides the identification of the sector number) are stored in a table for later referral. Upon completion of the calibration process, the process S180 terminates.
The disk drive 100 typically goes through the routine of generating the position offset values after each “power-on” sequence of the drive. Alternatively, the position offset values can be generated when then disk drive 100 is initially assembled and then stored in a non-volatile memory medium such as the disk 102.
In a further aspect of the present invention, the position offset values may also be stored on one or more dedicated tracks 192 on the disk 102 (see FIG. 9A). Upon powering on, the read element 166 will be directed by the servo controller 132 (see
Next, the process S200 advances to process step S206, where the write element 164 is first aligned with the centerline of the dedicated track 192 using the position offset information stored in memory 140. The process S200 then writes the position offset information on the dedicated track 192. Other system parameters, such as the read/write channel parameters, may also then be stored on the dedicated track 192. Note that during the process S200, the read element 166 is off the track centerline while the write element 164 is aligned with the track centerline.
During the power-up process S220, as shown in
Through the use of the present invention, the skew or position offset information used in the alignment of a read element of an MR head may be provided and stored, so that the read element of an MR head may be accurately aligned with the centerline of written data during a read operation, without any additional calibration.
While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specific constructions and arrangements shown and described, since various other modifications may occur to those ordinarily skilled in the art.
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|US20100134917 *||Apr 9, 2009||Jun 3, 2010||Kabushiki Kaisha Toshiba||Method and apparatus for offset control in a disk drive|
|U.S. Classification||360/77.08, 360/77.04|
|International Classification||G11B20/20, G11B5/596|