WO1998052195A1 - Procede destine a etre utilise dans une unite de disque pour etalonner le gain demodulateur sans conversion a/n du signal d'erreur de position composite (cpes) - Google Patents

Procede destine a etre utilise dans une unite de disque pour etalonner le gain demodulateur sans conversion a/n du signal d'erreur de position composite (cpes) Download PDF

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Publication number
WO1998052195A1
WO1998052195A1 PCT/US1998/008335 US9808335W WO9852195A1 WO 1998052195 A1 WO1998052195 A1 WO 1998052195A1 US 9808335 W US9808335 W US 9808335W WO 9852195 A1 WO9852195 A1 WO 9852195A1
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WO
WIPO (PCT)
Prior art keywords
head
track
pes
servo
pesoffset
Prior art date
Application number
PCT/US1998/008335
Other languages
English (en)
Inventor
Kelly Douglas Wright
Original Assignee
Iomega Corporation
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 Iomega Corporation filed Critical Iomega Corporation
Publication of WO1998052195A1 publication Critical patent/WO1998052195A1/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
    • G11B21/00—Head arrangements not specific to the method of recording or reproducing
    • G11B21/02—Driving or moving of heads
    • G11B21/10—Track finding or aligning by moving the head ; Provisions for maintaining alignment of the head relative to the track during transducing operation, i.e. track following

Definitions

  • the present invention relates generally to servo loop calibration techniques, and more particularly to a servo loop calibration technique that saves cost by eliminating the need for an A/D conversion of the composite position error signal (CPES) in a disk drive in order to calibrate the gain of the head position transducer, commonly known as the demodulator.
  • CPES composite position error signal
  • the presently preferred embodiments of the invention relate to a servo loop calibration method and circuit useful in accurately controlling the track following in a disk drive. Therefore, although the invention may be used in other applications, the background of the invention will be discussed with reference to a disk drive.
  • a closed loop control system may be configured as shown in Figure 1.
  • a summing device 14 and controller circuit 10 are utilized to control a physical plant or process, which in this case is a magnetic recording system 12.
  • the controlled variable Y(t) is compared to a reference input X(t) .
  • the reference input X(t) may be the position of a particular track on a disk, and the controlled variable may be the position of the read/write head of the magnetic recording system.
  • This error signal is provided as an input to the controller 10.
  • Controller 10 is a dynamic system added to the loop to stabilize and enhance the closed-loop system characteristics.
  • the output of controller 10 is an actuating signal A(t), which changes as a function of the error signal E(t) .
  • the actuating signal A(t) is developed to correct the recording system 12, e.g., to control the position of a read/write (R/W) head over a desired track.
  • the controller circuit 10 contains the control strategy for the entire servo control system. Within the control circuit 10 is a compensation component (s) . Typical goals of a controller are (1) to position a read/write head over a given disk track as quickly as possible and (2) to hold it over the track as accurately as possible. The position of the read/write transducer is controlled by the servomechanism in accordance with signals from the read/write electronics of the system.
  • hard disk drives examine the magnitude of A/D samples from both (A-B) and (C-D) and look for the condition
  • (A-B) j j (C-D) j . But again this is different from using a sign comparator instead of an A/D, as in the present invention.
  • one known servo system employs an A/D convertor to feed digitized samples of a composite position error signal (CPES) to a control processor.
  • a primary goal of the present invention is to save cost by replacing the A/D convertor with a less expensive sign comparator.
  • the use of an A/D converter to provide feedback to the control processor adds to the production cost of disk drive units. While A/D devices are relatively inexpensive on a per-unit basis, the requirement of such a device for each disk drive can add hundreds of thousands or even millions of dollars to the manufacturer's total production costs, depending on the number of units produced. Thus, the need for this A/D convertor is a disadvantage to manufacturers of disk drives and other devices requiring motor control.
  • the present invention provides a servo system for use in a disk drive in controlling the position of a read/write (R/W) head with respect to tracks of a disk so as to avoid inadvertent over-writing of data of a neighboring track.
  • the disk drive includes means (14A, 32) for generating a position error signal (PES) indicative of the error, if any, in the position of the head (see Fig. 3) .
  • PES position error signal
  • the inventive servo system comprises a controller (10) and a sign comparator (42) , and the controller is programmed to perform a calibration sequence to determine a value of the offset signal (PESOFFSET) corresponding to PES when the read/write head is at the l/4-track head position, and in subsequent track following operations to use this known relationship to accurately control and monitor the position of the read/write head with respect to a given data track.
  • the sign comparator is coupled to the controller and provides signals to the controller indicative of the sign of the CPES.
  • the controller is programmed to alternately obtain samples of (A-B) signals (50) and (C-D) signals (52) , and to determine a first sum of outputs of the sign comparator corresponding to the (A-B) samples and a second sum of outputs of the sign comparator corresponding to the (C-D) samples.
  • the controller is further programmed to determine a value of the offset signal (PESOFFSET) that will cause the first and second sums to be equal.
  • the present invention also provides a servo method for use in a disk drive.
  • the method includes steps for performing an initial demodulator calibration procedure whereby a demodulator gain or slope (K DEM0D ) is determined.
  • K DEM0D demodulator gain or slope
  • the width of the read/write head is an integral term of the demodulator gain.
  • the calibration procedure comprises (1) alternately obtaining, via the R/W head, position samples from the (A-B) and (C-D) signals; (2) generating a position error signal (PES) from said samples, wherein PES includes a square wave component; (3) activating the track following control system with said PES that includes a square wave component which will cause the average track following head position to converge to a 1/4 track position and will result in the square wave component of PES having an amplitude that alternates between a positive value and a negative value that corresponds to a l/4-track head position error; (4) forming a composite position error signal (CPES) by summing the PES with an offset signal (PESOFFSET) , wherein PESOFFSET has a square wave component whose amplitude is adjustable and whose phase is opposing the phase of the square wave component of PES, (5) monitoring the sign of CPES and determining a first sum of outputs of the sign comparator corresponding to the (A-B) samples and a second sum of outputs
  • Figure 1 schematically depicts a servo control system.
  • Figure 2 schematically depicts a known format of a servo burst pattern of a disk.
  • Figure 3 schematically depicts how a disk drive servo system may be modified in accordance with the present invention to replace an A/D converter with a simple sign comparator for monitoring the sign of the composite position error signal.
  • Figures 4A-4C depict exemplary waveforms useful in explaining the operation of the present invention.
  • Figure 4A depicts the idealized demodulator characteristic of the preferred embodiment
  • Figure 4B illustrates the slope of the exemplary idealized demodulator characteristic
  • Figure 4C depicts the square wave component of the position error signal.
  • Figures 5A-5C depict additional waveforms useful in explaining the operation of the present invention.
  • Figure 5A is an exemplary plot of frequency of CPES values corresponding to (A-B) and (C-D) samples;
  • Figure 5B illustrates how the frequency plots of Figure 5A are changed via the square wave component of the PESOFFSET signal;
  • Figure 5C illustrates how the integral or sum of the sign comparator outputs intersect at the point at which the magnitude of the PESOFFSET signal equals the magnitude of the PES signal corresponding to a one-quarter track error.
  • the present invention is especially suited for use in conjunction with a disk having a servo pattern as (partially) depicted in Figure 2. As shown, a read/write
  • R/W head or transducer 16 is utilized to read servo burst signals ("A", "B” , "C” , “D” ) that are recorded in servo sectors of the disk.
  • the servo burst signals are arranged as shown, in a burst pattern generally denoted by reference numeral 20, such that the signals ("A") of the first set, denoted 22A, are disposed on one side of each track and the signals ("B") of a second set, denoted 22B, are situated on a side of the track opposite to "A” .
  • the "A" and “B” burst signals do not overlap their respective tracks.
  • a third set 24A of "C” bursts and a fourth set 24B of "D” signals overlap the tracks such that, for example, the "C” signals overlap every other track (such as tracks 26A and 26C) whereas the "D" signals overlap the tracks not covered by the “C” signals, as shown.
  • a first track 26B is marked by adjacent burst signals “A” and “B” and further by overlapping burst signals “D” .
  • a second track 26C is marked by adjacent bursts "A” and “B” and overlapping "C” bursts .
  • a third track 26D is like the first track 26B insofar as the layout of the "A", "B” , "C” and "D” burst signals are concerned.
  • the PES for a sample obtained from the "A” and “B” bursts is formed by taking the average amplitude detected from the "A" burst and subtracting the average amplitude detected from the "B” burst, represented by (A-B) .
  • (C-D) is similarly a difference of average amplitudes detected from the "C” and “D” bursts.
  • A-B difference signal
  • C-D difference of average amplitudes detected from the "C” and "D” bursts.
  • a grey scale track number may be embedded in servo data (not depicted herein) to unambiguously identify the track number. This can help the controller to be able to distinguish tracks, such as track 26A and track 26C, that are surrounded by an identical layout of servo burst signals. See the repeating nature of the idealized demodulator characteristic shown in Fig. 4A. )
  • Figure 3 schematically depicts the general architecture of the servo system utilized in Iomega
  • Figure 3 illustrates how this arrangement may be modified in accordance with the present invention to save cost.
  • the prior servo system may be modified by replacing the analog-to-digital (A/D) convertor 40 with a simple sign comparator 42. Cost is saved because the sign comparator 42 is a significantly less expensive component than the A/D convertor 40.
  • A/D analog-to-digital
  • a servo control system in accordance with the present invention comprises the following components: a controller 10, which may be implemented with a microprocessor, digital signal processor (DSP) , or the like; a pair a digital-to-analog (D/A) convertors 30A, 30B; a position error signal (PES) demodulator 32; a zero order hold circuit 34; an analog compensator circuit 36; an actuator 38; the simple sign comparator 42; amplifiers 44A, 44B and 44C; and summing devices 14A, 14B and 14C.
  • the simple sign comparator 42 e.g., may output a single digital bit of information which is a "1" value when its input is zero or positive and a "0" value when its input is negative. In this respect, it is significantly less complicated, and expensive, than the A/D convertor 40 since the latter outputs a multiple digital bit representation of the actual value (magnitude) of its input.
  • the servo control system of Figure 3 may be implemented as an electromechanical circuit.
  • the actual track position (“Ptrk”) is input to summing device 14A along with the head position ("Phd") .
  • the position error (“Perr") is equal to Ptrk - Phd.
  • the position error, Perr is a mechanical signal input to the demodulator 32.
  • the demodulator 32 outputs an electrical signal, i.e., the PES signal, which is proportional to the head position error.
  • the demodulator 32 has a gain, K DEM0D .
  • the PES signal output by the demodulator 32 is input to the summing device 14B and summed with the PESOFFSET signal generated by the controller 10.
  • Samples of the PES signal are stored temporarily in the zero order hold (ZOH) device 34.
  • the output of the ZOH is referred to as the composi te position error signal, or CPES.
  • CPES composi te position error signal
  • the sign (+ or -) of each sample of the CPES signal is monitored by the sign comparator 42.
  • the CPES signal is input to the analog compensator 36.
  • the output of the analog compensator circuit, V TF is summed with a seek signal, V SEEK , and fed via amplifier 44C to actuator 38.
  • the general mode of operation of a servo control system of the kind depicted in Figure 3 will be apparent to one of ordinary skill in designing disk drive servo systems, and so the non-essential details of the system are not described herein.
  • the demodulator 32 is defined by a "characteristic" function that determines the output PES value for a given input Perr value. The particular characteristic that is applicable at a given time depends upon whether the Perr value is based on an (A-B) sample or a (C-D) sample.
  • the square wave component of CPES described above can be eliminated by outputting a corresponding inverted phase square wave on PESOFFSET.
  • the amplitude of the PESOFFSET square wave corresponds to the 1/4 -track position, it will equal the amplitude of the PES square wave signal and will cancel the square wave component of PES.
  • the PESOFFSET amplitude corresponding to the l/4-track position is detected, in accordance with the present invention, without the use of an A/D convertor. Instead, a simple sign comparator that provides a signal indicative of the sign (positive or negative) of CPES is used in conjunction with the random noise that exists on the PES signal.
  • a simple sign comparator that provides a signal indicative of the sign (positive or negative) of CPES is used in conjunction with the random noise that exists on the PES signal.
  • PESOFFSET "ZERO" VALUE 1/2 ⁇ (
  • PESOFFSET j where ⁇ SGN(C-D) 0)
  • the magnitude of the square wave on PESOFFSET that corresponds to the 1/4 track position can be obtained either from the point at which the two curves of Figure 5C cross each other or, assuming symmetrical curves and non zero offsets in the sign comparator, or analog compensator's, integrator, from the average of the two PESOFFSET magnitude values described above, i.e., from the midpoint between where the two curves cross the x axis ( j PESOFFSET

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  • Moving Of The Head To Find And Align With The Track (AREA)

Abstract

L'invention porte sur un servo système destiné à être utilisé dans une unité de disques en réglant la position d'une tête de lecture/écriture par rapport aux sillons d'un disque de façon à éviter les risques de superposition d'écriture des données sur un sillon voisin. L'unité de disques génère un signal d'erreur de position (PES) indiquant l'erreur éventuelle dans la position de la tête. Le servo système comprend un contrôleur (10) et un comparateur (42) de signes. Le contrôleur est programmé pour réaliser une séquence d'étalonnage de façon à déterminer une valeur de décalage de signal d'erreur de position (PESOFFSET) correspondant à une erreur de position de tête d'1/4 de sillon dans le signal d'erreur de position, et dans les opérations ultérieures de suivi de sillon, à utiliser cette relation connue entre le signal d'erreur de position (PES) et son décalage (PESOFFSET) pour régler et contrôler avec précision la position de la tête de lecture/écriture par rapport à un sillon de données spécifique. PES et PESOFFSET sont ajoutés pour créer un signal d'erreur de position composite (CPES). Le comparateur de signes est couplé au contrôleur et envoie un signal au contrôleur indiquant le signe de CPES.
PCT/US1998/008335 1997-05-13 1998-04-24 Procede destine a etre utilise dans une unite de disque pour etalonner le gain demodulateur sans conversion a/n du signal d'erreur de position composite (cpes) WO1998052195A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US85515097A 1997-05-13 1997-05-13
US08/855,150 1997-05-13
US93104897A 1997-09-16 1997-09-16
US08/931,048 1997-09-16

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WO1998052195A1 true WO1998052195A1 (fr) 1998-11-19

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6160012A (en) * 1997-05-23 2000-12-12 Schering Aktiengesellschaft Leukotriene B4 derivatives, in particular oximo-LTB4 - antagonists
SG99952A1 (en) * 2000-08-15 2003-11-27 Seagate Technology Llc Servo test method
US6760170B2 (en) 2000-08-15 2004-07-06 Seagate Technology Llc Servo test method

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0420693A2 (fr) * 1989-09-29 1991-04-03 International Business Machines Corporation Système de stockage de données sur disque avec un système de positionnement de la tête
EP0471314A1 (fr) * 1990-08-17 1992-02-19 Quantum Corporation Servosystème à positionner d'une tête de balayage de disques
US5400201A (en) * 1993-10-25 1995-03-21 Syquest Technology, Inc. Servo burst pattern for removing offset caused by magnetic distortion and method associated therewith
US5760990A (en) * 1995-08-08 1998-06-02 Seagate Technology, Inc. Servo position error signal calibration in a hard disc drive

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0420693A2 (fr) * 1989-09-29 1991-04-03 International Business Machines Corporation Système de stockage de données sur disque avec un système de positionnement de la tête
EP0471314A1 (fr) * 1990-08-17 1992-02-19 Quantum Corporation Servosystème à positionner d'une tête de balayage de disques
US5400201A (en) * 1993-10-25 1995-03-21 Syquest Technology, Inc. Servo burst pattern for removing offset caused by magnetic distortion and method associated therewith
US5523902A (en) * 1993-10-25 1996-06-04 Syquest Technology, Inc. Servo burst pattern for removing offset caused by magnetic distortion and method associated therewith
US5760990A (en) * 1995-08-08 1998-06-02 Seagate Technology, Inc. Servo position error signal calibration in a hard disc drive

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6160012A (en) * 1997-05-23 2000-12-12 Schering Aktiengesellschaft Leukotriene B4 derivatives, in particular oximo-LTB4 - antagonists
SG99952A1 (en) * 2000-08-15 2003-11-27 Seagate Technology Llc Servo test method
US6760170B2 (en) 2000-08-15 2004-07-06 Seagate Technology Llc Servo test method

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Publication number Publication date
TW454179B (en) 2001-09-11

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