CA2127971C - Method and apparatus for phase modulated servo positioning in a direct access storage device - Google Patents
Method and apparatus for phase modulated servo positioning in a direct access storage deviceInfo
- Publication number
- CA2127971C CA2127971C CA002127971A CA2127971A CA2127971C CA 2127971 C CA2127971 C CA 2127971C CA 002127971 A CA002127971 A CA 002127971A CA 2127971 A CA2127971 A CA 2127971A CA 2127971 C CA2127971 C CA 2127971C
- Authority
- CA
- Canada
- Prior art keywords
- servo
- signal
- phase
- tracks
- disk surface
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/16—Digital recording or reproducing using non self-clocking codes, i.e. the clock signals are either recorded in a separate clocking track or in a combination of several information tracks
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
- G11B5/58—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B5/596—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on disks
- G11B5/59605—Circuits
- G11B5/59622—Gain control; Filters
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
- G11B5/58—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B5/596—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on disks
- G11B5/59683—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on disks for magnetoresistive heads
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
- G11B5/58—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B5/596—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following on disks
- G11B5/59688—Servo signal format patterns or signal processing thereof, e.g. dual, tri, quad, burst signal patterns
Abstract
A phase modulated servo method and apparatus are provided for use in a disk file. The disk file includes at least one disk mounted for rotation about an axis and the disk has at least one disk surface for storing data. At a predefined location of the disk surface a series of servo tracks of a predetermined high gain servo pattern are written. The predetermined high gain servo pattern includes 360° phase difference information within each data cylinder. The servo tracks are detected for identifying servo phase information.
Description
212'~971 ~THOD A~D APPARATUS ~OR PHAS~ M~DULATeD SXRVO
PD8ITT~ IN A DIR~CT ACC~SS STORAG~ D~vIce RA~.RnUND OF THE INVENTION
1. Field of the Invention The present invention relates generally to a phase modulated servo positioning system in a direct acces~ storage device (DASD) and more particularly to a phase modulated ~ervo method and apparatus for u~e with tr~n~ cer head~ having instabilities.
PD8ITT~ IN A DIR~CT ACC~SS STORAG~ D~vIce RA~.RnUND OF THE INVENTION
1. Field of the Invention The present invention relates generally to a phase modulated servo positioning system in a direct acces~ storage device (DASD) and more particularly to a phase modulated ~ervo method and apparatus for u~e with tr~n~ cer head~ having instabilities.
2. De~cription of the Prior Art Computers often include auxiliary memory ~torage units having media on which data can be written and from which data can be read for later use. Disk drive units incorporating stacked, commonly rotated rigid magnetic disk3 are used for storage of data in magnetic form on the di~k surface~. Data i8 recorded in concentric, radially spaced data information tracks arrayed on the ~urfaces of the disk~. Transducer heads driven in a path toward and away from the drive axi~ write data to the di3k~ and read data from the disks.
All DASD unit~ must have a method to position each data head over the proper radial location to write a track and again, to position it very close to the ~ame location to read the track. With the higher level files using a voice coil type of actuator, a feedhack -ch~n; I must be provided to locate and stably hold the head on a given track. Typically, track accessing and trac~ following are provided utilizing a magnetically written pattern in the DASD unit. A dedicated servo ~ystem employs one ~urface of one of the di~ks in the DASD on which to have all the tracking and acces~ information. A
sector ~ervo ~ystem u~es ~mall portions of tracks between each or between ~everal ~ectors on each track of each data surface to provide the tracking and acces~ information. A hybrid servo system uses both to obtain advantage~ of each type of ~ervo.
212~971 Magneto-resiative (MRi) heads are a great advanf - ~ in read/write technology for DASD; however, the MR head~s wor~t characteristics iu head in~tability. The term head in~tability is used to describe a number of reA~h~k waveform ahnorr~litie~. Although the exact cause o~ head lnstability ia not known, the mo~t popular model states that head instability is due to non-linear ch~ngea in the transfer curve of the MR element. The~e jumps may be due to non-linear changes in magnetic domain v~ - L in the MR ~ L.
The jumps in the transfer curve cause corresponding jumps in the re~hack waveform. Most importantly, the non-linear features of the element transfer curve change each time the head i8 excited. The excitation typically is due to writing data, but can al~o be due to landing the MR head on the disk, hitting an asperity on the disk or ~hAng;ng MR bias current.
A problem exist~ to generate a position error signal ~PES) from a pha~e --- lated ~PM) ~ervo pattern in the p e~ence of magnetic recording head instability. When in~tabilitie~ are pre~ent in the reA~hA~k signal, a PES
generated from a phase modulated ~PM) servo signal can result in a track miaregistration ~TMR) error.
SUMMARY OF THE INVENTION
It i~ a principal object of the present invention to provide a phase - ~ated servo method and apparatus for use with trAna3~cer head~ having instabilities that overc -~ many of the disadvantages of prior art arreng --t~. -In brief, the objects and advantagea of the present invention are achieved by a phase modulated ~ervo method and apparatua used in a disk file.
The di~k file includes at leaat one disk mounted for rotation about an axis and the disk has at least one disk surface for storing data. At a predefined location of the disk surface a plurality of ~ervo tracks of a predet~ in~d high gain servo pattern are written. The predetq- ; n~d high gain servo pattern includes 360~ phase difference information within each data cylinder.
The servo tracks are detected for identifying servo phase information.
.
BRIEF DESCRIPTION OF THE DRAWING
- ':
:
2:12'7971 . ~
Ro9-93-034 3 The present invention, together with the above and other object~~ and advantage~7, can be~t be understood from the following detailed de~cription of the F '~ L of the invention illustrated in the drawing, wherein:
FIG. 1 is a schematic and block diagram of a data ~torage disk file embodying the present invention;
FIG. 2 is a diagram showing the acces~ing --h;7ni~ for a single disk ~urface of the apparatus of FIG. l;
FIG. 3 i~ a block diagram epre~entation illustrating apparatus for carrying out the servo demodulation method according to the present invention in the data ~7torage di~k file of FIG. l;
FIG. 4 i~ a chart illu~trating a stable rea~'ha~k signal and a rea~7hack 3ignal with instabllity shown in dotted line;
FIG. 5 i9 a chart illustrating a high gain servo pattern for reference tracks of the invention together with a standard gain servo pattern.
DETAILED DESCRIPTION OF THE ~REr~h~i~ EMBODIMENTS
In FIG. 1 there is shown a partly schematic block diagram of parts of a data ~torage disk file 10 including a data ~torage medium generally designated as 12 and a control unit generally designated as 14. In the preferred em-~o~ L of this invention, the data ~torage medium 12 i9 ~ d in a rigid magnetic disk drive unit 12, although other ?-h~n;c~lly moving memory configurations may be used. Unit 12 is illustrated in ~implified form sufficient for an understanding of the present invention bec~l7~e the utility of the present invention is not limited to the details of a particular drive unit construction.
Referring now to FIGS. 1 and 2 of the drawing~, disk drive unit 12 include~ a ~tack 16 of disk~ 18 having at lea.~t one magnetic surface 20. The ! disk~ 18 are ted in parallel for simultaneou~ rotation on and by an inte-212797~
grated spindle and motor assembly 26. Data information on each disk 18 are read and/or written to by a corresponding tr~n~ cer head 28 movable acros~
the disk surface 20.
Tran~dl10sr head~ 28 are mounted on flexure springs 30 carried by arms 32 ganged together for simultaneous pivotal v~ - ~ about a support spindle 34.
one of the arma 32 includes an extenaion 36 driven in a pivotal motion by a head drive motor 38. Although several drive arran~ are : ~lly used, the motor 38 can include a voice coil motor 40 cooperating with a magnet and core assembly ~not seen) operatively controlled for moving the tr~n~duc~r heads 28 in synchroni3m in a radial direction in order to position the heads in regiatration with data information track~ or data cylinder~ 42 to be followed and access particular data sectors 44. Data storage disk file 10 is a modular unit including a housing 46. The variou~ component~ of the disk file 10 are controlled in operation by signals generated by control unit 14 such as motor control signals on line 26A and position control signals on line 38A.
Numerous data information tracks 42 each at a specific radial location are arrayed in a concentric pattern in the magnetic medium of each disk aurface 20 of data disks 18. A data cylinder includes a set of coLre~on~ing data information track~ 42 for the data surfaces 20 in the data storage disk file 10. Data information tracks 42 include a plurality of segments or data sectors 44, each cont~ining a predefined size of individual groups of data records which are saved for later retrieval and updates.
The data information tracks 42 are di~posed at predet~r~in~d positions relative to a servo reference index. In FIG. 2 one sector 44 is illustrated as SECTOR 0 with a fixed index or mark INDEX for properly locating the first data ~ector. The location of each next sector 44 i~ identified by a 3ector identification (SID) pulse read by tr~n~dllcer heads 28 from surfaces 20.
Referring to FIG. 3, there is shown a circuit diagram illu~trating phase modulated aervo apparatu~ for carrying out the phase modulated servo method of the invention generally designated by the reference numeral 50.
2~2797~
In accordance with a feature of the phase modulated servo method of the invention, servo phase information is obtained from a high gain servo pattern that i9 robust to MR head instability. Utilizing the high gain aervo pattern of the invention provide~ a modified waveform a~ compared to a conventional phase modulated servo pattern so that the baseline is min~ ~z~d and the error due to head instability can alao be min;~;7ed Additionally, for a given radial displA~e L of the actuator the high gain servo pattern provides a larger phase change, so that phase errors due to instability represent smaller displacement error~.
In FIG. 3 apparatus 50 includes a servo channel including a de~icated servo surface 20~ shown together with a dedicated servo tran~d~-cer head 28' coupled to a servo preamplifier (SPA) 52, an automatic gain control (AGC) 54 and a servo identification (SID) filter 56. A data channel includes a data trAn~d~ r head 28 di~posed adjacent a data surface 20, arm electronics (AE) 58, an automatic gain control (AGC) 60 and a servo filter 62. The phase information stored in the servo patterns is derived by extracting a flln~ Lal harmonic, such as 2.5 Mhz, from the rea~ha~ signal by the high-pa~s SID filter 56 and servo filter 62. Signals from either the de~ ted servo head 28' or servo patterns read by data trAn~du~r head 28, are multiplexed at an analog multiplexer block 64. A zero-crossing comparator detector 66 coupled to the multiplexer 64 detects the zero crossing in the rea~hack signal. The output of the comparator 66 is supplied to a servo phase ator 68.
Comparator 66 applies a square wave signal to the servo phase d -hlator 68 with precise phase transitions based on the zero crossings of the fir~t hA - ic signal. This square wave is then exclusive ORed or XORed with a 2.5 Mhz crystal oscillator and the transition differences beL... these two ~ignals are integrated over a certain period by ~ervo phase ' - lator 68. The integrator value at the end of this period is p opoLLional to the head offset relative to the track center line. This value i~ referred to as the position error signal (PES~.
Referring to FI&. 4, there i3 shown a stable reA~ha~ signal together with a rea~ha~k signal with instability shown in dotted line. When the MR
~- ' 21~'7~7~
, head 28 is used to read phase ;--- lated servo information, the most significant form of head instability is cau0ed by non-linear jumps in the transfer curve of the MR element. These jumps can occur anywhere along the transfer curve, and hence, anywhere wLthin the r~a~hark waveform. When the transfer curve jump causes a rea~hack waveform baseline shift as indicated at 400, a phase error can result from the detected zero crossing by comparator 66 and therefore a position error. This causes track misregistration or TMR.
When the non-linear jump in the transfer curve occur~ in the peak of the rea~h~k waveform, there is little shift in phase of the signal.
Referring to FIG. 5, a high gain servo pattern indicated by a bracket 500 and a standard gain servo pattern indicated by a bracket 502. In FIG. 5, the servo patterns 500 and 502 are shown with radius ~h~nge~ relative the vertical axis and cir~, 'e~enLial changes relative the horizontal axis. High gain refers to the angle of the magnetic transitions in the servo burst. The angle is greater for the high gain pattern; and therefore the phase chAnges faster for a given radial displacement. FIG. 5 shows the burst pattern for both the standard pha3e pattern that repeats in four tracks and the high gain pattern of the invention that repeats in one track. Since the angle of the pattern is increased by a factor of four, the signal-to-noise for the servo ch~nn~l is effectively i...pLoved by a factor of four. Since the high gain readback waveform does not flatten out at the baseline, the pe~cenL of time that the waveform that is at the baseline is reduced. Thi~ reduce3 the effect that jumps in the MR head transfer curve have on the detected pha#e of the rea~hark waveform.
While FIG. 3 ~hows circuitry 50 with a dedicated servo architecture with reference track~, it 3hould be understood that the invention applies to sector servo architectures as well. The dedicated servo surface 20' consists of tracks written on 1/2 cylinder spacings so that there are two servo half track~ for each data cylinder. Position is en~oded using the 3tandard servo pattern 502 on the surface 20' by ch~ngi ng the phase with a 2.5 MHz burst by 22.5 dey ae3 in each adjacent servo half track. There are 16 half tracks or 8 cylinders before the servo pattern 502 repeats. The dedicated surfaceincludes three regions of outer guard band, data band and inner guard band.
!
Data surfaces 20 include a pair of reference tracks consisting of a series of servo tracks written in the inner and outer guard band~ on each data surface. The reference tracks are simLlar to the dedicated servo pattern 502.
The reference tracks are written on 1/4 oyllnder tracks. The OD reference tracks are written with the servo pattern 500 that runs through 360 degrees of phase on one cylinder. The ID reference tracks and the dedicated surface servo pattern 500 repeat in 4 cylinders or tracks.
For DASD 10, the linear bit density is typically twice as high at the inner disk radiu~ as at the outer disk radius. This cau~e~ the ~eaAh~k waveform to have wide pulses at the ID and narrow pulses, resulting in a large percentage of baseline at the OD. With ~ ation reference tracks at both the disk OD and ID, the high gain pattern 500 i9 only needed at the outer ra-dius. The inner radius reference tracks use the four-trac-k- type standard servo pattern 502 to determine both the correct position c- _ ~ation for tracks near the ID and the course position _~~~ation for the OD. Then the correct position ~ ation for track~ near the OD is calculated by first applying the ~ ation measured at the ID and then reading the high gain pattern 500 and determin;ng the exact _ _- ~ation required.
The rea~h~ck waveform ba~el;ne is greatly reduced with the high gain pattern 500. This i8 due to the fact that the head 28 is ~- -lly reading three servo quarter tracks at a time. The rP~ha~k waveform is the linear sum of the signal from each quarter track where the standard servo pattern 502 re~hack = 0.5signal(0~) + signal(22.5~) + 0.5signal(22.5~); and where the high gain pattern 500 re~h~k = 0.5signal(0~) + signal(45~) ~ 0.5signal(90~).
While the invention has been described with reference to details of the illu~trated embodiments, these details are not intended to limit the scope of the invention as defined in the arpc~ded claims.
All DASD unit~ must have a method to position each data head over the proper radial location to write a track and again, to position it very close to the ~ame location to read the track. With the higher level files using a voice coil type of actuator, a feedhack -ch~n; I must be provided to locate and stably hold the head on a given track. Typically, track accessing and trac~ following are provided utilizing a magnetically written pattern in the DASD unit. A dedicated servo ~ystem employs one ~urface of one of the di~ks in the DASD on which to have all the tracking and acces~ information. A
sector ~ervo ~ystem u~es ~mall portions of tracks between each or between ~everal ~ectors on each track of each data surface to provide the tracking and acces~ information. A hybrid servo system uses both to obtain advantage~ of each type of ~ervo.
212~971 Magneto-resiative (MRi) heads are a great advanf - ~ in read/write technology for DASD; however, the MR head~s wor~t characteristics iu head in~tability. The term head in~tability is used to describe a number of reA~h~k waveform ahnorr~litie~. Although the exact cause o~ head lnstability ia not known, the mo~t popular model states that head instability is due to non-linear ch~ngea in the transfer curve of the MR element. The~e jumps may be due to non-linear changes in magnetic domain v~ - L in the MR ~ L.
The jumps in the transfer curve cause corresponding jumps in the re~hack waveform. Most importantly, the non-linear features of the element transfer curve change each time the head i8 excited. The excitation typically is due to writing data, but can al~o be due to landing the MR head on the disk, hitting an asperity on the disk or ~hAng;ng MR bias current.
A problem exist~ to generate a position error signal ~PES) from a pha~e --- lated ~PM) ~ervo pattern in the p e~ence of magnetic recording head instability. When in~tabilitie~ are pre~ent in the reA~hA~k signal, a PES
generated from a phase modulated ~PM) servo signal can result in a track miaregistration ~TMR) error.
SUMMARY OF THE INVENTION
It i~ a principal object of the present invention to provide a phase - ~ated servo method and apparatus for use with trAna3~cer head~ having instabilities that overc -~ many of the disadvantages of prior art arreng --t~. -In brief, the objects and advantagea of the present invention are achieved by a phase modulated ~ervo method and apparatua used in a disk file.
The di~k file includes at leaat one disk mounted for rotation about an axis and the disk has at least one disk surface for storing data. At a predefined location of the disk surface a plurality of ~ervo tracks of a predet~ in~d high gain servo pattern are written. The predetq- ; n~d high gain servo pattern includes 360~ phase difference information within each data cylinder.
The servo tracks are detected for identifying servo phase information.
.
BRIEF DESCRIPTION OF THE DRAWING
- ':
:
2:12'7971 . ~
Ro9-93-034 3 The present invention, together with the above and other object~~ and advantage~7, can be~t be understood from the following detailed de~cription of the F '~ L of the invention illustrated in the drawing, wherein:
FIG. 1 is a schematic and block diagram of a data ~torage disk file embodying the present invention;
FIG. 2 is a diagram showing the acces~ing --h;7ni~ for a single disk ~urface of the apparatus of FIG. l;
FIG. 3 i~ a block diagram epre~entation illustrating apparatus for carrying out the servo demodulation method according to the present invention in the data ~7torage di~k file of FIG. l;
FIG. 4 i~ a chart illu~trating a stable rea~'ha~k signal and a rea~7hack 3ignal with instabllity shown in dotted line;
FIG. 5 i9 a chart illustrating a high gain servo pattern for reference tracks of the invention together with a standard gain servo pattern.
DETAILED DESCRIPTION OF THE ~REr~h~i~ EMBODIMENTS
In FIG. 1 there is shown a partly schematic block diagram of parts of a data ~torage disk file 10 including a data ~torage medium generally designated as 12 and a control unit generally designated as 14. In the preferred em-~o~ L of this invention, the data ~torage medium 12 i9 ~ d in a rigid magnetic disk drive unit 12, although other ?-h~n;c~lly moving memory configurations may be used. Unit 12 is illustrated in ~implified form sufficient for an understanding of the present invention bec~l7~e the utility of the present invention is not limited to the details of a particular drive unit construction.
Referring now to FIGS. 1 and 2 of the drawing~, disk drive unit 12 include~ a ~tack 16 of disk~ 18 having at lea.~t one magnetic surface 20. The ! disk~ 18 are ted in parallel for simultaneou~ rotation on and by an inte-212797~
grated spindle and motor assembly 26. Data information on each disk 18 are read and/or written to by a corresponding tr~n~ cer head 28 movable acros~
the disk surface 20.
Tran~dl10sr head~ 28 are mounted on flexure springs 30 carried by arms 32 ganged together for simultaneous pivotal v~ - ~ about a support spindle 34.
one of the arma 32 includes an extenaion 36 driven in a pivotal motion by a head drive motor 38. Although several drive arran~ are : ~lly used, the motor 38 can include a voice coil motor 40 cooperating with a magnet and core assembly ~not seen) operatively controlled for moving the tr~n~duc~r heads 28 in synchroni3m in a radial direction in order to position the heads in regiatration with data information track~ or data cylinder~ 42 to be followed and access particular data sectors 44. Data storage disk file 10 is a modular unit including a housing 46. The variou~ component~ of the disk file 10 are controlled in operation by signals generated by control unit 14 such as motor control signals on line 26A and position control signals on line 38A.
Numerous data information tracks 42 each at a specific radial location are arrayed in a concentric pattern in the magnetic medium of each disk aurface 20 of data disks 18. A data cylinder includes a set of coLre~on~ing data information track~ 42 for the data surfaces 20 in the data storage disk file 10. Data information tracks 42 include a plurality of segments or data sectors 44, each cont~ining a predefined size of individual groups of data records which are saved for later retrieval and updates.
The data information tracks 42 are di~posed at predet~r~in~d positions relative to a servo reference index. In FIG. 2 one sector 44 is illustrated as SECTOR 0 with a fixed index or mark INDEX for properly locating the first data ~ector. The location of each next sector 44 i~ identified by a 3ector identification (SID) pulse read by tr~n~dllcer heads 28 from surfaces 20.
Referring to FIG. 3, there is shown a circuit diagram illu~trating phase modulated aervo apparatu~ for carrying out the phase modulated servo method of the invention generally designated by the reference numeral 50.
2~2797~
In accordance with a feature of the phase modulated servo method of the invention, servo phase information is obtained from a high gain servo pattern that i9 robust to MR head instability. Utilizing the high gain aervo pattern of the invention provide~ a modified waveform a~ compared to a conventional phase modulated servo pattern so that the baseline is min~ ~z~d and the error due to head instability can alao be min;~;7ed Additionally, for a given radial displA~e L of the actuator the high gain servo pattern provides a larger phase change, so that phase errors due to instability represent smaller displacement error~.
In FIG. 3 apparatus 50 includes a servo channel including a de~icated servo surface 20~ shown together with a dedicated servo tran~d~-cer head 28' coupled to a servo preamplifier (SPA) 52, an automatic gain control (AGC) 54 and a servo identification (SID) filter 56. A data channel includes a data trAn~d~ r head 28 di~posed adjacent a data surface 20, arm electronics (AE) 58, an automatic gain control (AGC) 60 and a servo filter 62. The phase information stored in the servo patterns is derived by extracting a flln~ Lal harmonic, such as 2.5 Mhz, from the rea~ha~ signal by the high-pa~s SID filter 56 and servo filter 62. Signals from either the de~ ted servo head 28' or servo patterns read by data trAn~du~r head 28, are multiplexed at an analog multiplexer block 64. A zero-crossing comparator detector 66 coupled to the multiplexer 64 detects the zero crossing in the rea~hack signal. The output of the comparator 66 is supplied to a servo phase ator 68.
Comparator 66 applies a square wave signal to the servo phase d -hlator 68 with precise phase transitions based on the zero crossings of the fir~t hA - ic signal. This square wave is then exclusive ORed or XORed with a 2.5 Mhz crystal oscillator and the transition differences beL... these two ~ignals are integrated over a certain period by ~ervo phase ' - lator 68. The integrator value at the end of this period is p opoLLional to the head offset relative to the track center line. This value i~ referred to as the position error signal (PES~.
Referring to FI&. 4, there i3 shown a stable reA~ha~ signal together with a rea~ha~k signal with instability shown in dotted line. When the MR
~- ' 21~'7~7~
, head 28 is used to read phase ;--- lated servo information, the most significant form of head instability is cau0ed by non-linear jumps in the transfer curve of the MR element. These jumps can occur anywhere along the transfer curve, and hence, anywhere wLthin the r~a~hark waveform. When the transfer curve jump causes a rea~hack waveform baseline shift as indicated at 400, a phase error can result from the detected zero crossing by comparator 66 and therefore a position error. This causes track misregistration or TMR.
When the non-linear jump in the transfer curve occur~ in the peak of the rea~h~k waveform, there is little shift in phase of the signal.
Referring to FIG. 5, a high gain servo pattern indicated by a bracket 500 and a standard gain servo pattern indicated by a bracket 502. In FIG. 5, the servo patterns 500 and 502 are shown with radius ~h~nge~ relative the vertical axis and cir~, 'e~enLial changes relative the horizontal axis. High gain refers to the angle of the magnetic transitions in the servo burst. The angle is greater for the high gain pattern; and therefore the phase chAnges faster for a given radial displacement. FIG. 5 shows the burst pattern for both the standard pha3e pattern that repeats in four tracks and the high gain pattern of the invention that repeats in one track. Since the angle of the pattern is increased by a factor of four, the signal-to-noise for the servo ch~nn~l is effectively i...pLoved by a factor of four. Since the high gain readback waveform does not flatten out at the baseline, the pe~cenL of time that the waveform that is at the baseline is reduced. Thi~ reduce3 the effect that jumps in the MR head transfer curve have on the detected pha#e of the rea~hark waveform.
While FIG. 3 ~hows circuitry 50 with a dedicated servo architecture with reference track~, it 3hould be understood that the invention applies to sector servo architectures as well. The dedicated servo surface 20' consists of tracks written on 1/2 cylinder spacings so that there are two servo half track~ for each data cylinder. Position is en~oded using the 3tandard servo pattern 502 on the surface 20' by ch~ngi ng the phase with a 2.5 MHz burst by 22.5 dey ae3 in each adjacent servo half track. There are 16 half tracks or 8 cylinders before the servo pattern 502 repeats. The dedicated surfaceincludes three regions of outer guard band, data band and inner guard band.
!
Data surfaces 20 include a pair of reference tracks consisting of a series of servo tracks written in the inner and outer guard band~ on each data surface. The reference tracks are simLlar to the dedicated servo pattern 502.
The reference tracks are written on 1/4 oyllnder tracks. The OD reference tracks are written with the servo pattern 500 that runs through 360 degrees of phase on one cylinder. The ID reference tracks and the dedicated surface servo pattern 500 repeat in 4 cylinders or tracks.
For DASD 10, the linear bit density is typically twice as high at the inner disk radiu~ as at the outer disk radius. This cau~e~ the ~eaAh~k waveform to have wide pulses at the ID and narrow pulses, resulting in a large percentage of baseline at the OD. With ~ ation reference tracks at both the disk OD and ID, the high gain pattern 500 i9 only needed at the outer ra-dius. The inner radius reference tracks use the four-trac-k- type standard servo pattern 502 to determine both the correct position c- _ ~ation for tracks near the ID and the course position _~~~ation for the OD. Then the correct position ~ ation for track~ near the OD is calculated by first applying the ~ ation measured at the ID and then reading the high gain pattern 500 and determin;ng the exact _ _- ~ation required.
The rea~h~ck waveform ba~el;ne is greatly reduced with the high gain pattern 500. This i8 due to the fact that the head 28 is ~- -lly reading three servo quarter tracks at a time. The rP~ha~k waveform is the linear sum of the signal from each quarter track where the standard servo pattern 502 re~hack = 0.5signal(0~) + signal(22.5~) + 0.5signal(22.5~); and where the high gain pattern 500 re~h~k = 0.5signal(0~) + signal(45~) ~ 0.5signal(90~).
While the invention has been described with reference to details of the illu~trated embodiments, these details are not intended to limit the scope of the invention as defined in the arpc~ded claims.
Claims (10)
1. Apparatus for demodulating a phase modulated servo signal in a disk file, said servo signal having a baseline, said apparatus comprising:
at least one disk mounted for rotation about an axis and having at least one disk surface for storing data;
means for writing at a predefined location of said disk surface a series of servo tracks of a predetermined high gain servo pattern, said high gain servo pattern producing a readback signal where the baseline is minimized;
said predetermined high gain servo pattern including 360° phase difference information within each servo track; said predetermined high gain servo pattern providing said readback signal having a predetermined high phase change for a predetermined radial displacement and said readback signal being at the baseline a predetermined small percent of time, whereby said readback signal does not flatten out at the baseline;
means for detecting said servo tracks for identifying servo phase information; and means for demodulating a phase modulated servo signal.
at least one disk mounted for rotation about an axis and having at least one disk surface for storing data;
means for writing at a predefined location of said disk surface a series of servo tracks of a predetermined high gain servo pattern, said high gain servo pattern producing a readback signal where the baseline is minimized;
said predetermined high gain servo pattern including 360° phase difference information within each servo track; said predetermined high gain servo pattern providing said readback signal having a predetermined high phase change for a predetermined radial displacement and said readback signal being at the baseline a predetermined small percent of time, whereby said readback signal does not flatten out at the baseline;
means for detecting said servo tracks for identifying servo phase information; and means for demodulating a phase modulated servo signal.
2. Apparatus for demodulating a phase modulated servo signal as recited in claim 1 wherein said means for writing at said predefined location of said disk surface said series of servo tracks of said predetermined high gain servo pattern include means for writing said series of servo tracks on 1/4 data cylinder spacing and in an outer guard band of said disk surface.
3. Apparatus for demodulating a phase modulated servo signal as recited in claim 1 wherein said means for writing and for detecting said reference track includes a magneto-resistive (MR) transducer head.
4. Apparatus for demodulating a phase modulated servo signal as recited in claim 1 wherein said means for detecting said servo tracks for identifying servo phase information includes transducer means for generating said readback signal from said disk surface; filter means coupled to said transducer means for generating a first harmonic readback signal;
zero-crossing comparator means coupled to said filter means for identifying zero-crossings of said first harmonic readback signal.
zero-crossing comparator means coupled to said filter means for identifying zero-crossings of said first harmonic readback signal.
5. Apparatus for demodulating a phase modulated servo signal as recited in claim 1 wherein said means for writing at said predefined location of said disk surface said series of servo tracks of said predetermined high gain servo pattern includes means for writing two signals of the samefrequency having a predetermined phase difference between adjacent servo tracks.
6. Apparatus for demodulating a phase modulated servo signal as recited in claim 5 wherein said predetermined phase difference between adjacent servo tracks is 45°.
7. A phase modulated servo method used in a disk file including at least one disk mounted for rotation about an axis and having at least one disk surface for storing data, said method comprising the steps of:
writing at a predefined location of said disk surface a series of servo tracks of a predetermined high gain servo pattern, said servo pattern producing a readback signal having a base line where the baseline is minimized; and said predetermined high gain servo pattern including 360° phase difference information within each servo track; said predetermined high gain servo pattern providing said readback signal having a predetermined high phase change for a predetermined radial displacement and said readback signal being at the baseline a predetermined small percent of time, whereby said readback signal does not flatten out at the baseline;
detecting said servo tracks for identifying servo phase information; and demodulating a phase servo signal.
writing at a predefined location of said disk surface a series of servo tracks of a predetermined high gain servo pattern, said servo pattern producing a readback signal having a base line where the baseline is minimized; and said predetermined high gain servo pattern including 360° phase difference information within each servo track; said predetermined high gain servo pattern providing said readback signal having a predetermined high phase change for a predetermined radial displacement and said readback signal being at the baseline a predetermined small percent of time, whereby said readback signal does not flatten out at the baseline;
detecting said servo tracks for identifying servo phase information; and demodulating a phase servo signal.
8. A phase modulated servo method as recited in claim 7 wherein said writing step includes the steps of:
writing said series of servo tracks on 1/4 data cylinder spacing and in an outer guard band of said disk surface.
writing said series of servo tracks on 1/4 data cylinder spacing and in an outer guard band of said disk surface.
9. A phase modulated servo method as recited in claim 7 wherein said disk file includes a dedicated servo surface containing a plurality of servo tracks of standard gain servo pattern and wherein said series of servo tracks is written in an outer guard band of said disk surface and further includes the step of: writing at an inner guard band of said disk surface a series of servo tracks of said standard gain servo pattern.
10. A direct access storage device comprising:
a housing;
at least one disk mounted in said housing for rotation about an axis and having at least one disk surface for storing data;
transducer means mounted for movement across said disk surface for reading and writing data and predefined types of servo identification patterns to said disk surface;
means for writing at a predefined location of said disk surface a series of servo tracks of a predetermined high gain servo pattern, said servo pattern producing a readback signal having a baseline where the baseline is minimized;
and said predetermined high gain servo pattern including 360° phase difference information within each servo track; said predetermined high gain servo pattern providing said readback signal having a predetermined high phase change for a predetermined radial displacement and said readback signal being at the baseline a predetermined small percent of time, whereby said readback signal does not flatten out at the baseline;
means for detecting said servo tracks for identifying servo phase information; and means for demodulating a phase servo signal.
a housing;
at least one disk mounted in said housing for rotation about an axis and having at least one disk surface for storing data;
transducer means mounted for movement across said disk surface for reading and writing data and predefined types of servo identification patterns to said disk surface;
means for writing at a predefined location of said disk surface a series of servo tracks of a predetermined high gain servo pattern, said servo pattern producing a readback signal having a baseline where the baseline is minimized;
and said predetermined high gain servo pattern including 360° phase difference information within each servo track; said predetermined high gain servo pattern providing said readback signal having a predetermined high phase change for a predetermined radial displacement and said readback signal being at the baseline a predetermined small percent of time, whereby said readback signal does not flatten out at the baseline;
means for detecting said servo tracks for identifying servo phase information; and means for demodulating a phase servo signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US12595993A | 1993-09-23 | 1993-09-23 | |
| US125,959 | 1993-09-23 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2127971A1 CA2127971A1 (en) | 1995-03-24 |
| CA2127971C true CA2127971C (en) | 1999-01-12 |
Family
ID=22422253
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002127971A Expired - Fee Related CA2127971C (en) | 1993-09-23 | 1994-07-13 | Method and apparatus for phase modulated servo positioning in a direct access storage device |
Country Status (12)
| Country | Link |
|---|---|
| US (1) | US6426844B1 (en) |
| EP (1) | EP0645764B1 (en) |
| JP (1) | JPH07169032A (en) |
| KR (1) | KR100191903B1 (en) |
| CN (1) | CN1064168C (en) |
| AT (1) | ATE197852T1 (en) |
| BR (1) | BR9403557A (en) |
| CA (1) | CA2127971C (en) |
| DE (1) | DE69426345T2 (en) |
| ES (1) | ES2152972T3 (en) |
| MY (1) | MY113278A (en) |
| SG (1) | SG47385A1 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2635942B2 (en) * | 1994-02-10 | 1997-07-30 | インターナショナル・ビジネス・マシーンズ・コーポレイション | Method and apparatus for servo positioning of direct access storage devices |
| JP3670440B2 (en) * | 1997-05-20 | 2005-07-13 | 富士通株式会社 | Position detection method on disk, disk device, and disk |
| US6961203B1 (en) * | 2001-03-06 | 2005-11-01 | Maxtor Corporation | Hybrid printed servo patterns for magnetic media and hard disk systems implementing same |
| JP2002373411A (en) * | 2001-06-15 | 2002-12-26 | Fuji Photo Film Co Ltd | Magnetic recording medium and drive apparatus thereof |
| JP4148951B2 (en) | 2005-01-12 | 2008-09-10 | 株式会社東芝 | Magnetic recording / reproducing device |
| JP2006221773A (en) * | 2005-02-14 | 2006-08-24 | Fuji Photo Film Co Ltd | Disk shape magnetic recording medium |
| US7209314B2 (en) * | 2005-06-09 | 2007-04-24 | Hitachi Global Storage Technologies Netherlands B.V. | Disk drive with phase-quadrature servo pattern and demodulated position error signal insensitive to timing and phase-misalignment errors |
| KR100771881B1 (en) * | 2006-08-23 | 2007-11-01 | 삼성전자주식회사 | Method for correcting phase of data sector according to disc rotational slip and disc drive using the same |
Family Cites Families (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5693119A (en) * | 1979-12-25 | 1981-07-28 | Nec Corp | Servo system for magnetic disk device |
| JPS56145568A (en) * | 1980-04-15 | 1981-11-12 | Mitsubishi Electric Corp | Head positioning system |
| US4549232A (en) * | 1983-06-27 | 1985-10-22 | International Business Machines Corporation | Phase modulated servo system |
| JPS60129708A (en) | 1983-12-16 | 1985-07-11 | Matsushita Electric Ind Co Ltd | Polarizing plate |
| US4598327A (en) * | 1985-06-28 | 1986-07-01 | International Business Machines Corporation | Servo control system using servo pattern time of flight for read/write head positioning in a magnetic recording system |
| JPS62175924A (en) * | 1986-01-28 | 1987-08-01 | Fujitsu Ltd | Off-track compensating system |
| JPS6398820A (en) * | 1986-10-15 | 1988-04-30 | Sony Corp | Recording system for magnetic disk |
| US5119248A (en) | 1987-10-30 | 1992-06-02 | Brier Technology, Inc. | Method of recording servo signals |
| JPH01220101A (en) | 1988-02-29 | 1989-09-01 | Hitachi Maxell Ltd | Moving multi-track head type information recorder |
| US5055951A (en) | 1989-03-10 | 1991-10-08 | Irwin Magnetic Systems, Inc. | Method and apparatus for servo-positioning movable transducer heads |
| US5185681A (en) | 1990-09-28 | 1993-02-09 | Seagate | Thermal offset compensation for high density disk drives |
| JPH04252415A (en) * | 1991-01-28 | 1992-09-08 | Matsushita Electric Ind Co Ltd | Magnetic disk and magnetic disk device |
| JP3082174B2 (en) * | 1991-04-04 | 2000-08-28 | ソニー株式会社 | Magnetic disk and its driving device |
| JPH05242435A (en) * | 1992-02-27 | 1993-09-21 | Hitachi Ltd | Magnetic disk device and head |
-
1994
- 1994-07-13 CA CA002127971A patent/CA2127971C/en not_active Expired - Fee Related
- 1994-08-29 MY MYPI94002268A patent/MY113278A/en unknown
- 1994-08-30 CN CN94115592A patent/CN1064168C/en not_active Expired - Fee Related
- 1994-08-30 KR KR1019940021533A patent/KR100191903B1/en not_active IP Right Cessation
- 1994-08-31 JP JP6206191A patent/JPH07169032A/en active Pending
- 1994-09-06 SG SG1996000355A patent/SG47385A1/en unknown
- 1994-09-06 ES ES94480084T patent/ES2152972T3/en not_active Expired - Lifetime
- 1994-09-06 DE DE69426345T patent/DE69426345T2/en not_active Expired - Fee Related
- 1994-09-06 EP EP94480084A patent/EP0645764B1/en not_active Expired - Lifetime
- 1994-09-06 AT AT94480084T patent/ATE197852T1/en not_active IP Right Cessation
- 1994-09-14 BR BR9403557A patent/BR9403557A/en not_active IP Right Cessation
-
1995
- 1995-09-11 US US08/526,197 patent/US6426844B1/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0645764B1 (en) | 2000-11-29 |
| US6426844B1 (en) | 2002-07-30 |
| MY113278A (en) | 2002-01-31 |
| EP0645764A3 (en) | 1996-09-11 |
| EP0645764A2 (en) | 1995-03-29 |
| KR950009677A (en) | 1995-04-24 |
| DE69426345D1 (en) | 2001-01-04 |
| CN1064168C (en) | 2001-04-04 |
| DE69426345T2 (en) | 2001-05-17 |
| CA2127971A1 (en) | 1995-03-24 |
| BR9403557A (en) | 1995-06-20 |
| SG47385A1 (en) | 1998-04-17 |
| ES2152972T3 (en) | 2001-02-16 |
| JPH07169032A (en) | 1995-07-04 |
| CN1110824A (en) | 1995-10-25 |
| KR100191903B1 (en) | 1999-06-15 |
| ATE197852T1 (en) | 2000-12-15 |
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