WO2005010870A1 - Guidage d'un capteur au moyen d'un profile lateral sensiblement courbe - Google Patents

Guidage d'un capteur au moyen d'un profile lateral sensiblement courbe Download PDF

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Publication number
WO2005010870A1
WO2005010870A1 PCT/US2003/020723 US0320723W WO2005010870A1 WO 2005010870 A1 WO2005010870 A1 WO 2005010870A1 US 0320723 W US0320723 W US 0320723W WO 2005010870 A1 WO2005010870 A1 WO 2005010870A1
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WIPO (PCT)
Prior art keywords
profile
sensor
parametric
curved
model
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Application number
PCT/US2003/020723
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English (en)
Inventor
Reed Hanson
John Morris
Thomas Zirps
Nathaniel Wilson
Brent Harmer
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Seagate Technology Llc
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Seagate Technology Llc filed Critical Seagate Technology Llc
Priority to AU2003304377A priority Critical patent/AU2003304377A1/en
Priority to PCT/US2003/020723 priority patent/WO2005010870A1/fr
Publication of WO2005010870A1 publication Critical patent/WO2005010870A1/fr

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Classifications

    • 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
    • G11B5/59627—Aligning for runout, eccentricity or offset compensation
    • 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
    • G11B5/54—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 into or out of its operative position or across tracks
    • G11B5/55—Track change, selection or acquisition by displacement of the head
    • G11B5/5521—Track change, selection or acquisition by displacement of the head across disk tracks
    • G11B5/5526—Control therefor; circuits, track configurations or relative disposition of servo-information transducers and servo-information tracks for control thereof

Definitions

  • This application relates generally to guidance systems, and more particularly to systems in which a significant parametric gradient may exist orthogonal to the sensor's nominal direction of travel.
  • a sensor is moved in a nominally longitudinal direction relative to a frame of reference.
  • a position scale is defined in a "generally lateral" direction relative to the longitudinal motion.
  • the broadly curved lateral profile is defined in terms of the generally lateral position scale, the scale(s) and the profile(s) both being part of a parametric model that is used to guide the sensor.
  • a parameter of interest is measured at many (N) positions across the position scale so as to generate at least N measurements.
  • the curved parametric profile is then expressed as a function based on the position scale and fewer than N/2 scalar coefficients, the scalar coefficients at least partially based on the measurements.
  • a position- indicative value is measured.
  • the model is used to generate a predicted position-indicative value.
  • a parameter of interest is measured at N positions across the position scale so as to express a preliminary profile of many measurements. Each of the measurements has a preliminary measurement error.
  • a servo controller then generates a curved parametric profile value between two successive ones of the N positions, without performing any lateral linear interpolation (i.e. along the generally lateral scale).
  • the model's curved parametric profile is defined so as to attenuate the errors generally and/ or to have reduced measurement errors at most of the N positions.
  • the sensor guiding step includes a step of interpolating between the first curved parametric profile and a second curved parametric profile to obtain a longitudinally interpolated value. This step is useful for generating a parameter value at a non- profiled longitudinal position, or for using more than one nearby profile for determining the best estimated parametric value.
  • a device of the present invention includes a sensor able to move in a nominally longitudinal direction relative to a predetermined frame of reference. The device further includes a servo controller constructed and arranged to guide the sensor substantially based on a parametric model.
  • the model defines both (1) a generally lateral position scale affixed to the frame of reference and (2) a first curved parametric profile defined relative to the position scale and having two or more contiguous concavity ranges each wider than the sensor.
  • the position scale of the model is not merely translational.
  • the model may be sophisticated so that the "generally lateral" direction accounts for relative rotation or other curvilinear distortion experienced by the sensor.
  • the parametric model includes many additional parametric profiles distributed across a longitudinal range, the parametric model essentially consisting of a table of coefficients smaller than 1 kilobyte per sensor. Additional features and benefits will become apparent upon reviewing the following figures and their accompanying detailed description.
  • Fig. 1 shows a flowchart of a method embodiment of the present invention.
  • Fig. 2 shows a plot of a parametric profile relative to a generally lateral position scale, introducing concepts but not illustrating the present invention.
  • Fig. 3 is a more magnified plot showing how even a finely-graded piecewise-linear model can introduce significant errors into lateral profiles of smoothly-varying parameters.
  • Fig.4 shows a plot of a profile of the present invention.
  • Fig. 5 shows an example of an electromechanical system constructed to benefit from the present invention.
  • Fig. 6 shows an oblique view of a 3-dimensional plot of thousands of parametric value measurements for a system like that of Fig. 5.
  • Fig. 1 shows a flowchart of a method embodiment of the present invention.
  • Fig. 2 shows a plot of a parametric profile relative to a generally lateral position scale, introducing concepts but not illustrating the present invention.
  • Fig. 3 is a more magnified plot showing how even
  • FIG. 7 shows a lateral profile model of the present invention expressed as a 4 x 97 table, small enough to be stored feasibly in a nonvolatile memory space.
  • Fig. 8 shows a matrix that is useful for deriving the coefficient values to be inserted into a table like that of Fig. 7.
  • Fig. 9 shows a flowchart of a preferred method of the present invention, one tailored for use in configuring a disc drive.
  • a sensor is set in motion relative to a frame of reference 110, defining a nominally "longitudinal" direction of travel.
  • a position scale is defined in a generally lateral direction 115 in fixed relation to the frame of reference, the sensor having a nominal width relative to the scale.
  • a positioning-related indicator value is measured at each of N positions across the position scale 125. This defines a preliminary (partial) profile of many indicator measurements each having a measurement error.
  • a profile function is expressed 130 in terms of the position scale and several (fewer than N/2) scalar coefficients.
  • Scalar coefficients are selected so as to define a "broadly curved" indicator profile and so as to define a model having reduced measurement errors at most of the N positions 135.
  • “broadly curved” it is meant that the profile has one or more broad ranges of concavity, many times wider than the sensor's nominal width. Steps 125 through 135 are repeated so that the model contains many additional indicator profiles distributed across a longitudinal range 145. The resulting model is stored in a non-volatile memory space smaller than N bytes per profile 150. Note that optional resource-sparing features of the present invention are also appreciable in other contexts, for example, in transmitting part of the model within a bandwidth-limited computer system.
  • the sensor's lateral position is detected 155.
  • the two profiles are used to generate respective indicator values at the detected lateral positions 170. These values are then used to obtain the model's indicator value (e.g. by longitudinal linear interpolation 175) See Figs. 7&9 and their accompanying discussion below, for an example of how to use more than two profiles for a better-than-linear longitudinal interpolation. If a difference is detected between the model's value and a value derived from a local measurement 180, a control signal is generated that moves the sensor toward a desired lateral position based on the detected difference 185.
  • FIG. 2 shows parametric profile 290 relative to a generally lateral position scale 202.
  • Scale 202 has units that are proportional to a "track number," a term that basically identifies a lateral (radial) location on a rotary data storage disc surface.
  • track number a term that basically identifies a lateral (radial) location on a rotary data storage disc surface.
  • each track number was "binary normalized” by dividing the track number by 2 ⁇ N, where N is the smallest integer such that the total number of tracks on a disc surface does not exceed 2 ⁇ N.
  • this kind of normalization is simply implemented as a shift of N bits, which is computationally convenient.
  • the model's generally lateral position scale 202 could alternatively be selected in units of milliradians, microns, tracks, meters or similar units generally characterizing a position that is "generally lateral" relative to the sensor's (longitudinal) motion.
  • the vertical dimension in Fig. 2 is a modeled parameter 201 used in disc drive servo control called "Coherent Repeatable Run-Out (CRRO) Compensation Value.”
  • parameter 201 is an offset value having units of distance about equal to 1/4000 of a "nominal track width.”
  • modeled parameter 201 might instead depict elevation, wind velocity, magnetic flux, or any other generally continuous parameter of interest to motion control, expressed in suitable units.
  • Profile 290 is a simple "zoned" profile in which the parameter value of each point on profile 290 is equal to that of the nearest of the basis points along scale 202.
  • zoned profiles like 290 are that they often introduce huge errors at lateral positions about halfway between those of each successive pair of basis points.
  • Profile 291 reduces this problem somewhat by using another piecewise-linear model. Between a successive pair of the basis points 252,253, a linear-interpolation model is used to effectuate a line segment 262 in profile 291.
  • profile 291 is formed as a series of line segments 263,264,265,266.
  • Fig. 3 shows how other piecewise-linear models can also introduce significant errors into lateral profiles of smoothly-varying parameters. It shows parameter 201 plotted against scale 202 in a greatly magnified area near basis point 257.
  • a "generally lateral position scale" is defined with a regular increment 399 about 2 to 3 orders of magnitude wider than the sensor (e.g., about as wide as a few hundred tracks).
  • each of the points 311-317 is a corresponding point 321,322,323,324,325,326,327 along a smoothly-varying, downwardly-curved profile.
  • M interleaved with these (M) successive points 321-327 are many (M-l) successive offsets 383,384,385,386,387,388.
  • Fig. 3 clearly shows that these offsets change monotonically (e.g. decreasing steadily left to right) across many regular increments 399, so they define a continuous "concavity range" 399 having a width equal to that of many regular increments 398 wide.
  • each regular increment is 398 is several times wider than the nominal width 397 of the sensor 396.
  • a curved profile comprising points like 321-327 rather than a piecewise-linear profile comprising points like 311-317
  • Fig. 3 that is to say that the actual profile 390 is likely to have a smaller difference 391 (in average magnitude) from curved profile 320 than a difference 350 from a piecewise-linear profile 310 of similar complexity, especially near the places where the piecewise-linear model would have "seams.”
  • Fig. 4 shows a plot of parameter 201 versus scale 202, also showing the several basis points 252,253,254,255,256,257 of Fig. 2. Overlaid on the plot is a curved profile 494 of the present invention.
  • profile 494 has an upward concavity range 478 and downward concavity range 479, each contiguous.
  • a profile like 494 is preferably modeled with only 3 to 10 (and more preferably 4 to 7) stored coefficient values uniquely assigned to a particular longitudinal location. These stored coefficient values are then expanded into a complete profile according to a predetermined algorithm.
  • a predetermined algorithm such as a third order polynomial characterized in four coefficients, one of ordinary skill will readily be able to select a set of coefficients so as to embody a curved profile (like 494) that passes closely among points (like 452 to 457) derived from nearby measurements. This embodiment is unusual in several respects.
  • FIG. 5 there is shown a "top view” of a system 500 constructed to benefit from the present invention.
  • System 500 includes "top” cover 523 that cooperates with base 502 to form a sealed chamber.
  • Components supported in the chamber include a spindle motor 515 which rotates one or more data storage disc(s) 589 at hundreds or thousands of revolutions per minute. Information is written to and read from data surfaces on disc(s) 589 through the use of an actuator assembly 561, which rotates during a seek operation about a bearing shaft assembly 530.
  • Actuator assembly 561 includes one or more actuator arms 590 which extend above and below each of the disc(s) 589, with one or more flexures 593 extending from each of the actuator arms.
  • Mounted at the distal end of each of the flexures is a sensor 534 on an air-bearing slider enabling sensor 534 to fly in close proximity adjacent the corresponding surface of an associated disc 589.
  • Servo and user data travels through sensor 534 and flex cable 580 to control circuitry on controller board 506.
  • Controller board 506 is configured with circuits described below with reference to Fig. 4 and/ or to perform the method described above with reference to Fig. 1).
  • Flex cable 580 maintains an electrical connection by flexing as each sensor 534 seeks along its arcuate path between tracks on disc(s) 589.
  • the sensor motion is "longitudinal” as it follows a data track.
  • a seek between data tracks is a “lateral” motion, perpendicular to "longitudinal” within abut 20 degrees.
  • VCM voice coil motor
  • the overall track position of sensors 534 is controlled through the use of a voice coil motor (VCM), which typically includes a coil 522 fixedly attached to actuator assembly 561, as well as one or more permanent magnets 520 which establish a magnetic field in which coil 522 is immersed.
  • VCM voice coil motor
  • the controlled application of current to coil 522 causes magnetic interaction between permanent magnets 520 and coil 522 so that coil 522 moves.
  • actuator assembly 561 pivots about bearing shaft assembly 530 and sensors 534 are caused to move across the surfaces of the disc(s) 589 between the inner diameter and outer diameter of the disc(s) 589. Clamping stresses may distort a circular servo track, especially those generated when discs are written before insertion into a system like 500. Additional distortion can occur when the center of the data tracks does not coincide with the disc's axis of rotation. For these and other reasons, a sensor's positional run-out can be repeatable and consistent across many adjacent tracks. This is called “Coherent" Repeatable Run-Out (CRRO). For very fine tracks, it is much better to measure, model, and compensate for CRRO than to completely prevent it. Fig.
  • CRRO Coherent Repeatable Run-Out
  • FIG. 6 shows an oblique view of a plot 600 of thousands of CRRO measurements 699 for a system like that of Fig. 5.
  • One plotted measurement 699 is shown at each intersection between a measurement track 601 and a longitudinal position 602 on a given data surface.
  • the longitudinal direction 641 and lateral direction 642 are also shown.
  • the longitudinal positions 602 in plot 600 are perfectly radial and linear, rather than arcuate. Because actuator assembly 561 moves sensor 534 by rotating, however, the controlled “lateral" movement of sensor 534 at a given longitudinal position 602 is actually along an arc. This illustrates how the term "lateral" is used in this document to describe a generally lateral orientation, not necessarily one that is exactly perpendicular to the sensor's nominal direction of travel.
  • the model comprises the selected scale and profile(s) that are used in guiding the sensor's motion relative to a sensed frame of reference (e.g. a grid pattern marked onto a disc surface).
  • the vertical scale of CRRO measurements is greatly magnified for visibility, so that Fig. 6 somewhat resembles a topographical map of a badly distorted disc surface. Physically, the particular distortions shown indicate localized radial (lateral) position errors primarily due to disc clamping, off-center rotation and/ or thermal effects.
  • Fig. 7 shows a lateral profile model of the present invention.
  • the model is expressed as a table 700 small enough so that it is stored in a nonvolatile memory space of controller board 506. To make this feasible, table 700 stores all of the CRRO data initially needed for guiding one sensor in just 4 columns of 97 rows of one-byte cells. It is a remarkable achievement in present-day disc drive design to compress all of the coherent position error data needed to guide one sensor into 1-2 kilobytes. To store the data for plot 600, for example, 30 columns of 192 rows would ordinarily be required. More generally, lateral profile models of the present invention can be stored, transmitted and used in ways that were previously not feasible.
  • the first 96 rows 701,702,703,704, ... ,796 of table 700 each correspond to a longitudinal position (such as 602 of Fig. 6) at which a profile is defined.
  • the profile is a polynomial of the form
  • A(x) c 0 + c x x H H c n x"
  • A(x) is the CRRO value in fractional-track units like those of Fig. 2
  • the 'S are coefficients to be extracted from table 700.
  • the values in the profile-specific row are each multiplied by a corresponding value in the sensor-specific scaling row 797.
  • the value for co is obtained by multiplying values in column 780, for ci from column 781, for c 2 from column 782, and for C03 from column 783.
  • the modeled profile at the longitudinal position of row 701 is
  • a m (x) 152 + 12x - 12x 2 + 136 5 x 3 3 ( 2 )
  • This third order polynomial expresses a modeled profile at a predetermined longitudinal position, sector 0.
  • the scale with respect to which the profile is defined is a binary-normalized track number, just like that of Fig. 4.
  • A7o ⁇ (x) increases steadily to its maximum value (in the hundreds).
  • This general behavior is like that of Fig. 4 and of many of the radial CRRO profiles of Fig. 6, which reach their respective maxima near the surface's innermost track.
  • To control servo position effectively, is desirable to compare a just- measured position error against an expected value more than 96 times per disc revolution.
  • the 96 profiles expressed in table 700 only correspond to a subset of the total number of detectable servo marks on each track of the disc surface.
  • each sensor passes 288 servo marks per disc revolution.
  • table 700 happens to contain a profile for each third servo mark encountered by the sensor.
  • Fig. 8 shows a matrix 800 that is useful for deriving the coefficient values to be inserted into a table like that of Fig. 7.
  • the matrix elements are integer powers of the xi's, reflecting the fact that simple polynomials have been selected for this example.
  • the Xi's represent the generally lateral position scale values of the k basis points that are to be used at a given longitudinal position at which a profile is generated. For the profile of Fig. 4, for example, includes 12 such values ranging between 0 and 0.75.
  • n 3 in the simple example of Fig.4 but may be in the range of 4 to 7 more typically.
  • X only needs to be formed and inverted once per sensor in a typical system.
  • Fig. 9 shows a method 900 of the present invention comprising steps 905 to 995.
  • One or more servowritten disc(s) are mounted 910 into a disc drive (like 500 of Fig. 5).
  • the process is initialized 920 by positioning a selected sensor at a first zone boundary (i.e. basis position) and gathering Position Error Signal (PES) measurements:
  • PES Position Error Signal
  • the Discrete Fourier Transform (DFT) of the CRRO is computed 925 over the harmonics of interest as
  • the harmonics of interest are the first 32 integer multiples of the disc rotation frequency, in which most of the CRRO energy resides.
  • P ⁇ (z) is an M x 1 vector containing the resampled profile for the z m zone.
  • the particular elements may vary depending on the particular position monitoring application while maintaining substantially the same functionality.
  • the more detailed embodiments described above relate to data handling devices, other applications involving guidance can readily benefit from these teachings without departing from the scope and spirit of the present invention.
  • the selection of a suitable combination of calibration memory size, accuracy, and formula complexity is a trade-off. The best solution will depend on the application, and except as specified below, no particular solution to this trade-off is of critical importance to the present invention.
  • a selection of formulae will typically be available and readily derived, depending on the applicable geometry.
  • One of ordinary skill will be able to use the above description to make and use a variety of polynomial- or sinusoid-based or other implementations in light of the teachings above, without undue experimentation.

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  • Length Measuring Devices With Unspecified Measuring Means (AREA)

Abstract

Les problèmes inhérents au guidage d'un capteur au moyen d'un profilé paramétrique latéral linéaire par morceaux sont généralement évités si l'on utilise au moins un profilé sensiblement latéral et courbé (494). Un capteur est configuré pour se déplacer dans une direction essentiellement longitudinale par rapport à un cadre de référence (110). Une échelle de position est définie dans une direction sensiblement latérale, par rapport au mouvement longitudinal (115). Chaque profilé latéral sensiblement courbé est défini en fonction de son échelle de position correspondante, l'/les échelle(s) et le(s) profilé(s) faisant respectivement partie d'un modèle paramétrique pouvant servir à guider le capteur (145).
PCT/US2003/020723 2003-06-26 2003-06-26 Guidage d'un capteur au moyen d'un profile lateral sensiblement courbe WO2005010870A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU2003304377A AU2003304377A1 (en) 2003-06-26 2003-06-26 Guiding a sensor using a broadly-curved lateral profile
PCT/US2003/020723 WO2005010870A1 (fr) 2003-06-26 2003-06-26 Guidage d'un capteur au moyen d'un profile lateral sensiblement courbe

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Application Number Priority Date Filing Date Title
PCT/US2003/020723 WO2005010870A1 (fr) 2003-06-26 2003-06-26 Guidage d'un capteur au moyen d'un profile lateral sensiblement courbe

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4775903A (en) * 1986-10-14 1988-10-04 Hewlett-Packard Company Sampled servo seek and track follow system for a magnetic disc drive
US5136561A (en) * 1991-01-03 1992-08-04 Turguy Goker Disk drive with target track acquisition
EP0774754A2 (fr) * 1995-11-17 1997-05-21 Fujitsu Limited Dispositif de mémoire à disques
US6549364B1 (en) * 1999-12-15 2003-04-15 Samsung Electronics Co., Ltd. Optimization method and apparatus for a generalized fourier seek trajectory for a hard disk drive servomechanism
US6614618B1 (en) * 2000-03-31 2003-09-02 Western Digital Technologies, Inc. Disk drive with feed-forward control path that receives a reference position signal to apply a feed-forward command effort at a rate greater than a servo sampling rate

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4775903A (en) * 1986-10-14 1988-10-04 Hewlett-Packard Company Sampled servo seek and track follow system for a magnetic disc drive
US5136561A (en) * 1991-01-03 1992-08-04 Turguy Goker Disk drive with target track acquisition
EP0774754A2 (fr) * 1995-11-17 1997-05-21 Fujitsu Limited Dispositif de mémoire à disques
US6549364B1 (en) * 1999-12-15 2003-04-15 Samsung Electronics Co., Ltd. Optimization method and apparatus for a generalized fourier seek trajectory for a hard disk drive servomechanism
US6614618B1 (en) * 2000-03-31 2003-09-02 Western Digital Technologies, Inc. Disk drive with feed-forward control path that receives a reference position signal to apply a feed-forward command effort at a rate greater than a servo sampling rate

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