Patent Application
20120147497
The application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-277390 filed on Dec. 13, 2010, the entire contents of which are incorporated herein by reference.
1. Field
Embodiments described herein relate to a magnetic recording medium and a magnetic recording apparatus.
2. Description of the Related Art
With respect to methods for subdividing servo patterns in bit-patterned media (BPM), the coercive force due to demagnetizing fields in large surface area patterns is reduced since a magnetic layer of the BPM is a non-granular continuous layer. Magnetic reversal sometimes occurs due to shock, such as head contact, even when a servo pattern magnetic direction has been initially magnetized.
A known countermeasure therefore is to make the surface areas smaller by subdividing the servo pattern, thereby securing coercive force. For example, there is a description in JP-A-2010-55720 of an example of shifting division position in the radial direction when subdividing a preamble and burst pattern.
However, while there is a need for a countermeasure to reproduction waveform amplitude deterioration caused by servo pattern division there is no known method for achieving such a goal.
A general configuration that implements the various features of embodiments will be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments and not to limit the scope of the embodiments.
Explanation follows regarding an exemplary embodiment.
Explanation follows regarding a first exemplary embodiment, with reference to
The magnetic disk apparatus includes a disk enclosure 101 and a circuit board 120.
The disk enclosure 101 is a device that densely housing components such as the magnetic disk medium 1, an actuator 105 that includes a spindle motor 102, a magnetic head 103 and a voice coil motor (VCM) (not shown in the drawings), a head gimbal assembly 108, a carriage arm 106, a shaft 110, and a head amplifier 107. The magnetic disk medium 1 is mounted to the spindle motor (SPM) 102. The magnetic head 103 includes at least a recording (write) element (not shown in the drawings) for recording magnetic data on the magnetic disk medium 1 and/or a reproduction (read) element (not shown in the drawings) that acts to extract magnetic data recorded on the magnetic disk medium 1 as an electrical signal. The write element includes, for example, a write coil, a main magnetic pole layer, and an auxiliary magnetic pole layer. The write coil functions to generate magnetic flux. The main magnetic pole layer functions to collect the magnetic flux generated in the write coil, and throw the magnetic flux out towards the magnetic disk. The auxiliary magnetic pole layer functions to circulate the magnetic flux thrown off from the main magnetic pole layer through the magnetic disk. Examples of a read element include a magnetoresistive (MR) element. The magnetic head 103 is mounted to the head gimbal assembly 108 so as to be disposed facing the magnetic disk medium 1.
Various magnetic storage media, described later, can be employed as the magnetic disk medium 1. The end portion of the head gimbal assembly 108 not mounted with the magnetic head 103 is fixed to the distal end of the carriage arm 106. The carriage arm 106 can be made to perform a swinging movement about the shaft 110 as the axis of rotation using the VCM. The magnetic head 103 can be scanned in a substantially radial direction over the magnetic disk medium 1 using this swing movement. By positioning the magnetic head 103 at a desired recording track on the magnetic disk medium 1 the magnetic head 103 can write data to recording bits arrayed along a recording track on the magnetic disk medium 1, or can read data from the magnetic disk medium 1. The head amplifier 107 performs the role of recording on the magnetic disk medium 1 by flowing a current based on a recording signal 113 through the write element mounted to the magnetic head 103, or performs the role of converting magnetic data of the magnetic disk medium 1 detected by the read element of the magnetic head 103 into a reproduction signal 114,
The circuit board 120 includes: a read channel 116, a micro processor unit (MPU) 115, a spindle motor (SPM) driver 111, a voice coil motor (VCM) driver 112 and a disk controller 117. The read channel 116 either decodes the reproduction signal 114 (servo signal or data signal) from the head amplifier 107 and converts the signal into digital data, or performs the role of converting data designated for recording from the disk controller 117 into a recording signal 113 for driving the head amplifier 107.
The MPU 115 drives the VCM driver 112 based on digital data (servo data) of the servo signal decoded by the read channel 116 to perform positional control on the magnetic head 103, or drives the SPM driver 111 to perform rotation control of the magnetic disk medium 1.
The disk controller 117 instructs the MPU 115 to perform positioning of the magnetic head 103 according to a recording or reproduction command from a host computer 118, and performs the role of addressing the magnetic head 103 to the magnetic disk medium 1. The disk controller 117 transmits and receives digital data for recording or reproduction to and from the read channel 116, and operates to return the result to the host computer 118.
Explanation now follows regarding a magnetic recording medium, with reference to
Generally data regions 11 and servo regions 12 are disposed on the magnetic disk medium 1 alternately along the circumferential direction. Namely, the servo regions 12 are disposed intermittently along strip shapes of substantially circular circumferences having the center of the magnetic disk medium 1 at substantially at the center. The data regions 11 are disposed at portions where there are no servo regions 12 disposed along the strip shaped substantially circular circumferences.
The data regions 11 are regions for storing data. Data sectors 13 are storage regions for recording or reproduction in the data regions 11 disposed at fixed length (track pitch) periods along the circumferential direction. Magnetic dots (not shown in the drawings) are included in the respective data sectors 13. The shape and the layout of magnetic portions provided in the data regions 11 is called the data pattern.
The servo regions (servo sectors) 12 are provided in order to identify the position of the magnetic dots included in the data regions 11 (and in particular their position in the disk radial direction). The servo regions 12 include magnetic dots of various shapes and layouts, as described later. The shape of the servo regions 12 are circular arc shapes that form the head access path in the magnetic disk apparatus, with the circumferential direction length of the servo regions formed so as to increase in length proportionally to their radial positions. The shape and layout of the magnetic dots provided in the servo regions 12 is called the servo pattern.
When the magnetic disk medium is in a rotating state the magnetic head 103 acquires positional data of the magnetic head 103 by the magnetic head 103 reading a reproduction signal formed by the magnetic dots included in the servo regions 12. The magnetic head 103 is positioned relative to the tracks according to the positional data acquired by the magnetic head 103, enabling recording or reproduction to be performed to the magnetic region in the desired position on the data regions 11.
Plural of the magnetic dots (first magnetic dots) 41 are disposed at specific positions in the data regions 11. Data bits a are formed by scanning the magnetic head over the first magnetic dots 41 inside the magnetic disk apparatus. Disposed in “specific positions” refers to there being a fixed relationship to adjacent dots, namely the magnetic dots are disposed intermittently along the circumferential direction (the track direction). Normally the first magnetic dots are disposed with a fixed separation to adjacent first magnetic dots in the circumferential direction. An example of disposing in specific positions is a structure of magnetic dots, described later, formed with a nanoimprint method or photolithographic method. In contrast thereto, an example of not being disposed in specific positions is as an irregular structure of magnetic dots formed by dispersing magnetic particles in a non-magnetic body (called a granular structure).
The first magnetic dots 41 are, for example, formed from a polycrystalline ferromagnetic body, such as CoCrPt. A non-magnetic body 44 such as silica, alumina or air is disposed around the periphery of the first magnetic dots 41. Adjacent pairs of first magnetic dots 41 are isolated from each other by the presence of the non-magnetic body 44. The first magnetic dots 41 are respectively imparted with the desired magnetic field by the recording element in the magnetic disk apparatus. The magnetization of the first magnetic dots 41 due to the magnetic field is held in a state facing in the desired direction. The first magnetic dots 41 can thereby store magnetic data. The reproduction element reproduces the magnetic data recorded in the first magnetic dots 41. Different hatching is employed according to the directions of magnetization in
The servo regions 12 include magnetic portions 42 and non-magnetic portions 43. The magnetic portions 42 include both plural magnetic dots (second magnetic dots) (not shown in the drawings) and non-magnetic bodies (not shown in the drawings) disposed so as to wrap around the magnetic dots. The second magnetic dots and the non-magnetic bodies are described later. In patterned media, generally magnetization is in the same direction for all of the second magnetic dots. The non-magnetic portions 43 are formed from non-magnetic bodies. Data bits a are respectively formed according to the magnetization and non-magnetization by scanning the magnetic head over the magnetic portions 42 and the non-magnetic portions 43 in the magnetic disk apparatus.
The servo regions 12 in the magnetic disk medium can be classified according to function of use into synchronization signal generating portions 21, synchronization signal detection portions 22, address portions 23, and precision position detection portions 24.
The synchronization signal generating portions 21 act to regulate the amplification ratio of a signal amplifier and make the amplitude uniform prior to acquiring the servo data, and to generate a sampling timing of an Analog to Digital (A/C) Converter clock signal. The synchronization signal generating portions 21 are continuous in the radial direction in a range over the whole or part of the span from the inner periphery of the medium to the outer periphery, and include magnetic portions formed at fixed intervals around the circumferential direction.
The synchronization signal detection portions 22 are characteristic patterns indicating the start of servo data. The synchronization signal detection portions 22 are continuous in the radial direction in a range over the whole or part of the span from the inner periphery of the medium to the outer periphery, and include either a single magnetic portion of longer bit length along the circumferential direction than the synchronization signal generating portions 21 or plural magnetic portions for generating a default code of plural bit length.
The address portions 23 are ID patterns indicating the track number and the sector number for each of the servo frames. In the magnetic recording apparatus the track position for positioning the magnetic head is indicated. The address portions 23 include magnetic bodies and at circumferential direction positions for indicating the sector number the address portions 23 are continuous in the radial direction in a range over the whole or part of the span from the inner periphery of the medium to the outer periphery. At circumferential direction positions for indicating the highest order digits of the track number the address portions 23 are continuous in the radial direction in a range over the whole or part of the span from the inner periphery of the medium to the outer periphery. The address portions 23 are intermittent in the medium radial direction at circumferential direction positions for indicating the lower order digits of the track number.
The precision position detection portions 24 are provided in the magnetic recording apparatus for detecting displacement data of the position of the magnetic head from track center. Examples of the precision position detection portions 24 include an arrangement in which one or more types of magnetic pattern of particular shape and/or layout in the circumferential direction are disposed such that the respective magnetic patterns have even separations for each track in the medium radial direction. Another example of the precision position detection portions 24 is an arrangement across plural tracks in which the length direction is not parallel to the radial direction of the disk, to give a band shaped magnetic pattern (referred to below as a diagonal band shaped magnetic pattern).
The magnetic disk medium 1 is rotated at a fixed angular velocity to obtain a servo pattern reproduction signal (a) at fixed time intervals from the head amplifier. After high frequency noise components have been blocked by a low-pass filter 122 in the read channel 116 the servo pattern reproduction signal (a) is then A/D converted by an A/D converter 123. Variable gain 121 is then adjusted by a gain controller 125 based on the digitalized amplitude data so as to obtain the optimal amplitude.
Lead-in portions of the servo patterns are written with a fixed cycle pattern as the synchronization signal generating portions 21, such that a predetermined servo gate signal (b) is asserted to obtain sufficient wave number for a Phase Locked Loop (PLL) to converge.
When the servo gate signal (b) is asserted, the PLL is locked to the synchronization signal of the servo pattern reproduction signal, and an ADC clock signal (d), required for sampling the address portions and the precision position detection portions expressed by the servo pattern reproduction signal, is generated from a PLL circuit 124.
A servo sync mark pattern indicating the start of servo data is written at the trailing end of the synchronization signal generating portions of the servo patterns with either a fixed length bit or a characteristic code pattern bit. When this is detected a synchronization pattern detection signal (c) is asserted.
A synchronization signal detector 126 confirms assertion of the synchronization pattern detection signal (c), and then a reproduced address portion is demodulated by sending an address detection gate signal (e) to an address demodulator 127.
An address demodulation value (g) is identified when demodulation of a default length address portion has been completed, and the address demodulation value (g) is recorded as digital data in a register 129. This is followed by assertion of a burst gate signal (f), and demodulation of the precision position detection portions is started by a precision position demodulator 128.
When demodulation of the default length precision position detection portions has been completed a precision position demodulation value (h) is identified and recorded as digital data in a register 129.
The MPU 115 reads the address demodulation value (g) and the precision position demodulation value (h) stored in the registers by performing the above operations, performs computation for positional control of the magnetic head, and drives the VCM driver 112.
However servo signal deterioration becomes an issue of in related examples adopting this approach. When the read head passes at the position of the subdivisions this results in a deterioration in the reproduction waveform amplitude. Accordingly a method is required that can correctly detect a servo pattern without being affected by such deterioration due to subdivision.
Subdivision of the address pattern in a similar manner to the SAM pattern is effective for preventing magnetic reversal of the address pattern. However, it is important to have a method for making subdivisions according to simple rules in address patterns in which their pattern changes according to the radial direction position (address code).
In the present exemplary embodiment the address pattern is subdivided by utilizing the characteristics of Manchester encoding.
(1) First division is made with a first single subdivision unit formed from the second bit of the two bits resulting from expanding the first single bit of the address code with Manchester encoding, combined with the first bit of the two bits resulting from expanding the next single bit of the address code.
(2) Then following on from (1) the next pattern is subdivided at a position that differs by a specific number of track pitches in the radial direction, by performing a similar operation.
Due to the characteristics of Manchester encoding two types arise for the width of magnetic body patterns, when there is a “1”, and when there is a “11” formed by two “1”s next to each other. The location where a “11” appears only when the second bit of the two bits resulting from expanding a given single bit of the address code with Manchester encoding, and the first bit of the two bits resulting from expanding the next single bit of the address code with Manchester encoding, are both “1”.
Consequently, by performing subdivision as in (1) above, the entire width of both patterns of “1” and patterns of “11” are divided by subdivision according to simple rules, and cases do not arise where only a “1” of half a “11” width pattern is divided.
By sequentially shifting radial position for performing subdivision by a specific number of times the track pitch (for example 1×), as in (2), the influence from subdivisions when the head passes along a track to reproduce the address can be reduced.
As shown in
The way in which subdivision of the address pattern is performed when there are the subdivision units of (1) is not limited to (2). For example, division may be made every 2× servo track pitch Tp in the radial direction so as to divide alternately in the circular circumferential direction.
Furthermore, since the coercive force of the small surface area lower order bit patterns is already intrinsically higher, there is less need to perform subdivision thereon. It is therefore possible to not subdivide the pattern in a range from the lowest order bit up to a specific bit.
According to the above exemplary embodiment, an address pattern that changes according to the address code can be subdivided using simple rules.
As a result a SAM can be correctly and reliably detected independently of the radial position where the read head passes, as explained in the above example.
More specifically, address patterns that change according to radial direction position can be subdivided according to the simple rules by the following method.
(1) In subdivision of an address pattern in the middle of a servo pattern of a bit patterned media, a single subdivision unit is formed from the second bit of the two bits resulting from expanding a given single bit of the address code with Manchester encoding, combined with the first bit of the two bits resulting from expanding the next single bit of the address code.
(2) The next pattern is subdivided at a position that differs by a specific number of track pitches in the radial direction, by repeating a similar operation.
(3) Such subdivision is performed repeatedly such that after the address code has been finally divided from the first bit to the last bit, subdivision is then again made to the first bit of the address code at a radial position that differs by a specific number of times the track pitch.
(4) Is the processing of (1) in which subdivision is not performed to the address pattern corresponding to bit (s) in a range from the lowest order bit up to a specific number of bits in the address code.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-277390 | Dec 2010 | JP | national |
