WO1983001531A1 - Procede et dispositif de positionnement d'un transducteur utilisant un codage de servo-piste noyee et une commande par microprocesseur - Google Patents

Procede et dispositif de positionnement d'un transducteur utilisant un codage de servo-piste noyee et une commande par microprocesseur Download PDF

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Publication number
WO1983001531A1
WO1983001531A1 PCT/US1982/000683 US8200683W WO8301531A1 WO 1983001531 A1 WO1983001531 A1 WO 1983001531A1 US 8200683 W US8200683 W US 8200683W WO 8301531 A1 WO8301531 A1 WO 8301531A1
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WIPO (PCT)
Prior art keywords
servo
transducer
track
data
tracks
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PCT/US1982/000683
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English (en)
Inventor
Peripherals Data
Robert E. Nalley
Leonard R. Shenfield
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Peripherals Data
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Publication of WO1983001531A1 publication Critical patent/WO1983001531A1/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
    • G11B5/59633—Servo formatting

Definitions

  • the present invention relates to an improved system and technique for radially positioning a transducer relative to a rotating disc and for maintaining the transducer in the desired radial position during the rotation of the disc.
  • a primary requirement is that the servo data take up a minimum of the disc recording surface, since that area will be unavailable for the storage of other information.
  • a technique that has previously been used, and which is used with the present invention, is to provide the encoded servo data on such tracks in narrow radial sectors located on the disc surface. The remainder of the disc surface is then available for the storage of other information on data tracks.
  • the interspersed or "embedded" servo data is encoded on the magnetic disc so that any par ⁇ ticular servo or data track can be uniquely identified from the signals produced by a magnetic transducer sensing the servo data.
  • the recorded servo data must really perform two functions. It must assist the transducer positioning mechanism in accessing a selected data track and it must provide a means for enabling the transducer to follow the selected track with as little deviation as possible from the track during the rotation of the disc.
  • the presence of a reversal of magnetic flux or a magnetic transition at one location within the cell is taken to represent a binary digit zero while the occurence of the reversal or transition at the second location within the cell indicates the binary digit one.
  • the preferred code in that system is the Gray code so that 2 N tracks can be uniquely encoded when N is the number of cells provided for the track identification function in each servo track. The detection of this information provides coarse servo data that is used to position the transducer in approximate registration with a selected target track.
  • This fine positioning servo data comprises a magnetic transition SUMMARY OF THE INVENTION
  • the decoding scheme of the present invention allows for track identifi ⁇ cation to the nearest servo or data track, i.e., with a reso ⁇ lution of one-half of a track since the servo and data tracks are interspersed, the data tracks being located half-way between adjacent servo tracks.
  • the track accessing function is accom ⁇ plished by means of a single chip microprocessor which inter ⁇ prets the encoded servo data and controls the movement of the transducer.
  • the novel encoding sequence used in the present invention enhances the stability of the transducer positioning after a preselected track has been accessed. The enhanced resolution and stability are achieved, in practical systems, using a minimum of disc space and hardware components.
  • the present invention provides, in its preferred embodiment, sectored servo tracks interspersed with the data tracks on the magnetic disc.
  • Each narrow radial sector has a number of frames of servo data on each servo track to uni ⁇ quely identify the servo track within a group of adjacent servo tracks; the number of frames being equal to at least one-half the number of tracks in the group. If the disc contains more than one group of tracks, additional means are provided to identify the particular group to which the servo track belongs.
  • Each data frame consists of a recorded magnetic transition or reversal of magnetic flux which pro ⁇ vides servo information at either a first or second location within the data frame.
  • the preferred embodiment described herein also provides an additional recorded magnetic transi ⁇ tion at the beginning of each data frame as a synchronization signal.
  • the data tracks are located outside the narrow radial 2/1.
  • the unique code embedded in the data frames on each track includes, preferably, the requirement of a Gray code encoding, i.e., between the corresponding data frames on ad ⁇ jacent servo tracks, only one pair of corresponding data frames has magnetic transitions not located at the same relative locations within the two data frames.
  • a stricter requirement is im ⁇ posed in that in the adjacent data frames from different tracks within a servo sector, the relative location of the magnetic transitions within the corresponding data frames from the different servo tracks is allowed to change only once every N successive servo tracks where N is the number of data frames per servo track.
  • N is the number of data frames per servo track.
  • the present invention uses a dynamic comparator.
  • the synchronization signals detected by the transducer are negative going pulses while the servo data signals are positive going pulses.
  • the automatic gain controlled or buffered signal from the transducer therefore, has its threshold into the comparator set at a positive value, the synchronization signals do not enter the comparator, and the comparator thus compares only the positive going servo sig ⁇ nals from the transducer with a positive D.C. voltage equal to a fraction of the peak expected signals into the compar ⁇ ator.
  • a series of pulses will be produced at the comparator output.
  • a series of four pulses will therefore appear at the output of the comparator corresponding to the location of the signals within the four data frames of the particular servo track. If the transducer is posi ⁇ tioned between servo tracks, five output pulses will be produced from the dynamic comparator, two pulses being produced as the transducer passes over the data frame in which the locations of the signals differ for the corres- ponding data frames from the adjacent servo tracks. These series of four or five pulses serve as the clock for a shift register.
  • the data input to the shift register comprises a series of data signals that correspond temporally either to the first possible location for servo signals within the data frames or to the second possible location for servo signals within the data frames or to some predeter ⁇ mined combination of these.
  • the output of the shift regi ⁇ ster will then be a four or five digit binary number which uniquely identifies the particular servo track within a group or a data track interspersed with the servo tracks. Thus, track identification with a resolution of one-half of a track is accomplished. If the D.C. input to the compa ⁇ rator is set at one-fourth of the peak level of the largest expected positive signals, this resolution is plus or minus one-fourth of a track.
  • the use of multiple comparators having D.C. voltage inputs set at different levels can be used to produce clock signals for the shift register, and in so doing, the plus or minus one-fourth track figure can be reduced.
  • a unique feature of the present invention is the use of a microprocessor to control, using four main implemented algorithms, the movement of the transducer toward a selected data track at which it is desired to read or write information.
  • the microprocessor calculates the number of tracks separating the radial position of the transducer from the radial location of the target track and updates this information each time the transducer passes over a radial sector of embedded servo infor- ation using an algorithm denominated herein as the "track accumulation interrupt" algorithm.
  • the micropro- cessor accesses a "long seek" algorithm in which a signal is generated in order to move the transducer toward the target track at a velocity determined by the microprocessor from the track separation.
  • the signal generated by the microprocessor is applied to a digital to analog converter so that the appro- priate analog voltage to move the transducer at the desired velocity is provided to the actuator.
  • the value of this signal applied to the digital to analog converter is recalculated by the microprocessor using the long seek algorithm based on updated information acquired from the track accumulator inter- rupt algorithm.
  • the microprocessor initially accesses a "short seek" algorithm. Using this algorithm, the microprocessor modulates a switch which, when closed, allows an analog correction voltage dependent upon the distance of the transducer from the target track to be applied to the actuator. This voltage is the same one used to maintain the transducer on a particular data track once it has been accessed and microprocessor control of the transducer position has terminated.
  • a "seek termination" algorithm is used by the micro ⁇ processor, when, during the course of a long or short seek, it determines that the transducer is close to the target track. If the transducer remains close to the target track for a measured interval of time, the seek termination algorithm permits the microprocessor control of the transducer position ⁇ ing to be terminated. If, however, the microprocessor determines during the course of the seek termination algorithm that in fact the transducer has overshot the target track, it causes the transducer to reverse its direction of motion. Depending on the amount of overshoot, either the long seek or short seek algorithm will be accessed by the microprocessor. The micro ⁇ processor continues using the four implemented algorithms, the
  • BUREA OMPI track accumulator interrupt algorithm, the long seek algorithm, the short seek algorithm, and the seek termination algorithm until the transducer has accessed the target track.
  • the entire track accessing function is performed using a single chip micro ⁇ processor and the four implemented algorithms rather than the many logic chips and hardware components that have previously been used.
  • the encoding of the servo tracks previously described is used to enhance the stability with which a transducer can be maintained on a particular data track.
  • the peak values of the detected servo signals oc ⁇ curring at times corresponding to the two possible locations for servo information are compared.
  • This data frame is selected * so that the servo tracks adjacent to the selected targeted data track have different relative locations for their re ⁇ corded servo signals in this data frame.
  • the comparison is performed by circuitry whose output is zero when the transducer is correctly positioned on the selected data track since the detected servo signals corresponding to the data frame are equal.
  • the circuitry provides feedback to position the transducer over the selected data track. This circuitry is used while the microprocessor is controlling the transducer position with the short seek algorithm as well as after microprocessor control terminates. There is little chance that the trans ⁇ ducer will be positioned over the wrong data track as the next adjacent stable nulls are located 2N tracks on either side of the selected track as a result of the described encoding.
  • FIGUI.E 1 is a simplified block diagram of a mag ⁇ netic disc recording and reproducing system in which the present invention is incorporated.
  • -FIGURE 2 illustrates the two possible magnetic en ⁇ codings for a servo data frame on a magnetic disc using the preferred tribit encoding.
  • FIGURE 3 illustrates the signal from a transducer moving directly over a data frame on a servo track in which the A-phase tribit of FIGURE 2 has been encoded.
  • FIGURE 4 illustrates the signal from a transducer moving directly over a data frame on a servo track in which the B-phase tribit of FIGURE 2 has been encoded.
  • FIGURE 5 illustrates the signal from a transducer ov- ing along a data track between the two adjacent data frames on the adjacent servo tracks that are differently encoded.
  • FIGURE 6 is a table showing a preferred servo data encoding pattern for recording servo data on a plurality of adjacent servo disc tracks in accordance with the invention.
  • FIGURE 7 illustrates schematically a portion of a disc having a preferred servo data encoding pattern for recording servo data on a plurality of servo disc tracks in accordance with the invention.
  • FIGURE 8 is a series of graphs illustrating the de- tected signals obtained for different positions of the transducer in response to the servo data encoding pattern of FIGURES 6 and 7.
  • FIGURE 9 is a simplified block diagram for the de ⁇ coding scheme used for fractional track detection and identi- fication in the present invention.
  • FIGURE 10 is a table showing the output of the dynamic comparator used in the decoding scheme shown in FIGURE 9.
  • FIGURE 11 is a table showing the output of the shift register for the different servo and data tracks within a group. 10.
  • FIGURE 12 shows the typical analog output for a position detector with data track zero (DT 0.0) as the targeted track.
  • FIGURE 13 shows the typical analog output for a position detector with data track four (DT 4.0) as the targeted track.
  • FIGURES 14 through 17 are flow charts showing, in simplified form, the steps of the track accumulator interrupt algorithm, the long seek algorithm, the short seek algorithm and the seek termination algorithm respectively.
  • the present invention relates to a system and method c for accessing a transducer to a selected data track on a magnetic disc and for accurately maintaining the transducer in registration with the selected track during the relative rotation of the disc with respect to the transducer.
  • a microprocessor controlled transducer positioning servo system making use of the present invention achieves, using a minimum of disc space, high accuracy with respect to the detection and identification of the selected track and high reliability with respect to the maintaining of the transducer in alignment with the selected track, and uses a minimum of disc space and hardware to do so.
  • FIGURE 1 a rotatable magnetic disc 22 which con- tains information recorded on circumferential tracks on the surface of the disc is shown schematically. This in ⁇ formation is recorded on the disc 22 and may be reproduced from the disc 22 by means of a transducer 24 which responds to magnetic transitions or reversals of magnetic flux occur- ring in the surface of the disc 22.
  • the transducer 24 in order to position the transducer 24 over a selected circumferential track located on the surface of the disc 22, the transducer 24 is mounted on a carriage 26 which moves the transducer 24 radially with respect to the center of the disc 22.
  • An actuator 28 respon ⁇ sive to electronic signals controls the carriage movement.
  • a magnetic disc 22 has servo information encoded upon it in circumferential tracks located within radial sectors 30 of the disc surface, as shown in FIGURE 1.
  • working data or infor ⁇ mation is encoded onto the disc 22, also on circumferen ⁇ tial tracks.
  • these data tracks be located radially between the servo tracks so that a transducer is correctly radially aligned with a da .a track when it is radially equidistant from two adjacent servo track locations.
  • the encoded servo tracks are designated, within a group of uniquely encoded tracks, by half integer numbers, such as 0.5, 1.5, 2.5, etc.
  • tracks ST 7.5, ST 7.5', and 7.5" would all be identically encoded but would be distinguished from one another by means noting the particular group to which the track belonged.
  • the transducer 24 is positioned over successive radial sectors 30 of servo information.
  • the servo information acquired by the trans- ducer 24 as it passes over the radial sectors 30 is pro ⁇
  • a primary objective of any transducer positioning servo system depending upon servo information encoded on the disc alongside the working data is that the servo in ⁇ formation take up as little space on the disc as possible, as this space is unavailable for the storage of working data. Since a rotating magnetic disc on which information is recorded on tracks may contain from less than forty to more than several hundred different data tracks, uniquely identifying each track on the disc by means of servo infor ⁇ mation encoded on the surface would require too much space on the disc. In the preferred embodiment of the present in- vention, therefore, servo tracks in the radial sectors on the disc are grouped into groups of eight successively po ⁇ sitioned adjacent tracks and uniquely identified within the group by means of a magnetic encoding. .
  • a minimum number of tracks in such a group of tracks is determined by the maximum possible radial movement of the transducer 24 between successive radial sectors 30.
  • the radial distance covered by a group of uniquely encoded tracks should exceed twice the maximum possible radial movement of the transducer 24 between radial sectors 30.
  • a means for keeping track of which one of the simi ⁇ larly encoded tracks the transducer 24 is aligned with is re ⁇ quired.
  • a microprocessor 54 is used to accum ⁇ ulate the actual track numbers as the transducer 24 moves radially, thereby providing a means for identifying the particular group in which a particular track is located.
  • each track is uniquely encoded by servo information in the four data frames in order to en ⁇ able a transducer 24 to be accessed to a selected track with ⁇ in the group and to follow that track accurately.
  • each data frame consisting of a single tribit.
  • tribit encoding with each data frame consisting of a single tribit.
  • the use of tribit encoding on servo tracks in connection with positioning systems for transducers was described in U.S. Patent No. 3,691,543 issued to Mueller.
  • Each tribit consists of three possible locations for signals*. At the beginning of each tribit, a synchronization signal is recorded. The other two locations for signals are for servo information data and, in each tribit, a signal is recorded at either one or the other of these locations.
  • each tribit can be encoded in one of two possible ways.
  • FIGURE 2 illustrates the two possible magnetic encodings for a servo ( data frame on a magnetic disc 24 in which the described tribit encoding is used.
  • the magnetic flux ⁇ reverses direction at the beginning of each tribit, indi ⁇ cated in FIGURE 2 by SI and S2, to produce a synchronization signal.
  • the locations for possible servo information signals at which the magnetic flux would again reverse are at posi ⁇ tions Gl and G2 as shown in FIGURE 2.
  • the magnetic flux re ⁇ verses from negative to positive at the first location Gl for possible servo information.
  • the magnetic flux reverses from negative to positive at the second location G2 for pos ⁇ sible servo information.
  • the synchronization signals for adjacent tribits have the same polarity, which is opposite to the polarity of the servo information signals themselves which occur at either the first or second possible locations for servo information in each tribit.
  • each data frame on the servo tracks consists of either a single A-phase tribit or a single B-phase tribit.
  • FIGURES 3 and 4 illustrate, respectively, the signals resulting from a transducer 24 which is moving along a servo track directly over a data frame consisting of an A-phase tribit and a B- phase tribit.
  • a negative synchronization pulse of amplitude E p is produced when the transducer 24 passes over the flux reversal at position SI
  • a positive pulse of amplitude E_ is produced at either position Gl or G2 when the transducer 24 passes over those positions.
  • the transducer 24 If the transducer 24 is not radially positioned directly over a servo track, but instead is radially positioned equi ⁇ distant from two adjacent servo tracks, so that it is actually in radial alignment with a data track, the trans ⁇ ducer 24 will average the signals from the adjacent data frames on the two servo tracks. If the adjacent data frames are both encoded with the A-phase tribit, the transducer 24 .
  • each data frame within a radial sector on each of the servo tracks from a group of servo tracks is encoded with either the A-phase or B-phase tribit.
  • the table in FIGURE 6 shows a preferred encoding of the data frames on the servo tracks within a group. As shown in the 0 table in FIGURE 6, the encoding for successive servo tracks differs within only one pair of adjacent frames.
  • FIGURE 7 is a schematic representation of a portion of a radial sector 30 containing servo information.
  • the hori ⁇ zontal arrows represent the direction of magnetic flux with the vertical lines in each designated servo track repre ⁇ senting the positions of the reversals of the magnetic flux 5 or magnetic transitions.
  • a negative magnetic transition serving as a synchroni ⁇ zation signal occurs on each track at the positions labeled SO, SI, S2, and S3.
  • the mag ⁇ netic transition is indicated by a vertical line in the data track occurring at the second possible location for servo information within the data frame, i.e., at the location labeled G2, such as is shown for example with respect to data frame 0 for servo track ST 0.5.
  • the magnetic trans ⁇ ition occurs at the first location for servo information within the data frame, i.e., at the location labeled Gl, such as is shown for example with respect to data frame 1 of servo track ST 0.5.
  • FIGURE 8 the detected signals from a magnetic transducer 24 that is radially positioned over the various servo tracks in a group and over the interspersed data tracks while the magnetic disc 22 is rotating is shown.
  • a negative synchronization pulse of amplitude Ep occurs as shown in FIGURE 8.
  • a positive pulse of amplitude E p occurs in the first data frame (data frame 0) correspond ⁇ ing to the second possible location G2 at which a magnetic transition providing servo information could occur.
  • positive pulses of amplitude E_ occur at times corresponding to the first possible loca ⁇ tions Gl in those data frames.
  • the output from the transducer 24 will contain positive going pulses at times cor ⁇ responding to both Gl and G2 for one of the four data frames of an amplitude equal to E p /2.
  • This signal results from the transducer 24 being positioned between adjacent servo tracks rather than directly over either one so that the contribu- tion ⁇ from each of the adjacent data tracks to the signal are averaged.
  • one positive going pulse of ampli ⁇ tude E- per data frame occurs.
  • Fractional track identification is accomplished through use of the output signals from the transducer* 24 as it passes over a radial sector 30 and produces signals corresponding to a radial location with respect to the encoded servo tracks.
  • the output signals from the transducer 24 are processed in an automatic gain control circuit or buffer 34 shown in FIGURE 1 so that the negative going synchronization pulses have an amplitude of -4 volts. .
  • FIGURE 9 shows a portion of the block diagram of FIGURE 1.
  • the output of the automatic gain control circuit or buffer 34 shown in FIGURE 1 serves as an input to a dynamic comparator circuit 44.
  • the other input to the dynamic comparator 44 is a D.C. voltage equal to 1/4 of the peak positive pulse that can be expected from the automatic gain control circuit 34, i.e. , one volt. This voltage determines the threshold of the dynamic comparator 44; only those pulses entering the dynamic comparator 44 that have a value greater than the comparator threshold of one volt will produce an output signal from the dynamic comparator 44.
  • the output of the dynamic comparator 44 is digital so that pulses of fixed amplitudes are produced for all input pulses greater than one volt.
  • Synchronization pulses having a negative amplitude, produce, therefore, no output from the dynamic comparator 44.
  • the output pulses from the dynamic comparator 44 correspond to the location of the recorded servo signals within the data frames of the servo track or tracks over which the transducer is travelling.
  • These digitized servo pulses from the dynamic comparator 44 are used as clock pulses for a shift register 46.
  • the table in FIGURE 10 shows the location of the clock pulses produced at the output of the dynamic comparator 44 as a function of the times HI and H2 corresponding respec- 5 tively to the locations Gl and G2 of possible servo signals within each data frame.
  • the presence of an output from the dynamic comparator 44 at a time HI or H2 in any of the data frames is indicated in the table in FIGURE 11 by the letter C. 10
  • the data input or gate 48 to the shift register in the preferred embodiment, consists of a series of pulses cor ⁇ responding in time to the first locations Gl for the four data frames within a radial sector 30. This series of pulses is obtained from the synchronization signals.
  • the synchronization signals from the transducer 24 are detected by the sync detector circuit 56, which produces an output only for those signals entering it which have a larger negative amplitude than -E_/2.
  • the output of the sync detector 56 is delayed by time delay circuits 58 and 60 20 so that the output of time delay circuit 60 is a series of pulses corresponding in time to the first locations Gl for servo information within the data frames in a radial sector 30. This series of pulses is used as the Gl data input 48.
  • the shift register circuit 46 temporarily registers 25 the presence or nonpresence of pulses at the Gl data gate 48 during the occurrence of the clock pulses.
  • FIGURE 11 can best be understood with reference to FIGURE 10, which shows the presence or nonpre ⁇ ence of the clock pulses at the times corresponding to the possible occurrences of servo signals.
  • FIGURE 10 shows the presence or nonpre ⁇ ence of the clock pulses at the times corresponding to the possible occurrences of servo signals.
  • the first clock pulse occurs simul ⁇ taneously with a pulse from the Gl data gate so that a binary one is recorded and registered in QA and later shifted to QE.
  • the second clock pulse for data track DT 0.0 occurs at a time corresponding to the second location, G2, of data frame 0 at which time there is no input into the shift register from the Gl data input 48 since that input for the preferred embodi- ent consists of pulses occurring at times corresponding to the Gl locations of the data frames only.
  • a binary zero will be registered in register QA and eventually shifted to register QD.
  • the last three clock pulses of data track DT 0.0 occur at times corresponding to the Gl locations of data frames 1, 2, and 3 respectively so that binary ones will be registered in registers QC, QB, and QA respectively. Hence the binary number 10111 is registered for data track DT 0.0.
  • register QE remains empty while the data corre ⁇ - ponding to the first clock pulse is shifted only over to the QD register. Since the first clock pulse for track ST 0.5 occurs at a time corresponding to the second location of a possible servo signal in data frame 0, a binary zero is .
  • a unique binary number is produced for each servo track within a group of servo tracks and for the corresponding data tracks interspersed among those servo tracks.
  • An additional signal 52 originating from either the synchronization signals or from an additional magnetic transi ⁇ tion embedded upon the servo tracks of the disc 24 is used to dump the binary number in the shift register 46 into a track number decoder or memory circuit 50 where it is processed to produce a track identification number.
  • track identi ⁇ fication to the nearest one half of a track is achieved.
  • the track identification number proceeds to an interface and microprocessor unit 54, as shown in FIGURE 1, where it is com ⁇ pared to the number of the selected data track.
  • the accuracy of the frac ⁇ tional track detection is plus or minus 1/4 of a track.
  • This level of accuracy is achieved with a single dynamic compara ⁇ tor 44 whose threshold level is set at one-fourth the ex ⁇ pected peak input voltage of a positive pulse.
  • the input pulses to the dynamic comparator 44 (corresponding to the one data frame in which the two adjacent servo tracks have servo information signals located at different positions) have ampli- tudes of one-half of the peak expected input pulse amplitude, such as is shown in FIGURE 5. If the transducer 24 moves radially away from alignment with the data track by 1/4 of a track, one of the input pulses in the frame will increase 21.
  • the radial location of the transducer 24 may be identified to within plus or minus 1/4 of a track. Even greater accuracy is possible with the present in ⁇ vention through the use of additional hardware. Greater ac ⁇ curacy can be achieved by the use of multiple comparators mounted in parallel with different threshold voltages and by additional further signal processing equipment to combine the outputs of the comparators to produce a clock signal for the shift register.
  • the microprocessor unit 54 uses the track identification number to determine the number of tracks separating the trans ⁇ ducer 24 from the target track.
  • the microprocessor 54 causes a voltage to be applied to the actuator 28 in order to move the transducer 24 at a predeter ⁇ mined velocity toward the target track, the velocity being dependent upon the distance spearating the transducer 24 from the target track.
  • both the tachometer function i.e., the determination of the radial distance separating the target track from the transducer 24, and the velocity scheduler function, i.e., the determination of the velocity at which the transducer 24 is moved toward the I ! target track, are accomplished with software using a single chip microprocessor rather than with hardware components utilizing several or many logic chips.
  • the microprocessor 54 implements four main algorithms in order to appropriately position the transducer 24 radially along the disc 22 at a selected data track. These four algo ⁇ rithms are denominated the "track accumulator interrupt” algo ⁇ rithm, the "long seek” algorithm, the “short seek” algorithm and the “seek termination” algorithm.
  • the microprocessor contains in its memory the current radial location of the transducer 24. When it is desired to acce . a new radial location on the disc 22, the microprocessor 54 cal ⁇ culates the number of tracks separating the location of the trans ⁇ ducer 24 from the target track. Depending on this number, either long seek algorithm or the short seek algorithm is then accessed by the microprocessor 54.
  • the separation between the transducer 24 and the target track as determined by the microprocessor 54 is used in order to call from a table programmed into the memory of the microprocessor 54, a value related to the velocity with which it is desired to move the transducer 24 toward the target track.
  • This value is appropriatel scaled and applied by the microprocessor 54 to a digital to analog converter (DAC) 82.
  • the DAC 82 produces an analog output in response to the digital input from the microprocessor 54.
  • This analog ouput is applied to the actuator 28 through a buffer amplifier 84, a DAC 1 switch 86 controlled by the microprocessor 54 and a power amplifier 88.
  • the value of the signal applied to the DAC 82 is updated after the transducer 24 detects the embedded servo information from 8 successive radial sectors and calculates the radial distance travelled by the transducer 24 during the 8 sector time interval. This information is then used in the long seek algorithm in order to change the rate of movement of the transducer 24 toward the target track. When the transducer 24 is determined to be less than
  • the microprocessor 54 accesses the seek termination algorithm to determine whether in fact the transducer 24 has remained close to the target track 23.
  • the microprocessor 54 (or has overshot the target track. If it has remained close to the target track, the microprocessor 54, after 5 milli ⁇ seconds,* disables the track -accumulator interrupt algorithm and ceases to control the position of the transducer 24. The transducer 24 is thereafter maintained in its correct position by a comparison voltage applied through the position switch 90 from the sample and hold curcuit 70, as will be described.
  • a signal is applied to the DAC 82 in order to change the direction of motion of the trans ⁇ ducer 24.
  • the microprocessor 54 thereafter determines whether the transducer 24 has reversed its direction. If it has, the microprocessor 54 accesses either the long seek algorithm or the short seek algorithm, depending on the track separation, in order to move the transducer 24 toward the target track.
  • the short seek algorithm controls the opening and closing of the position switch 90. The closing of this switch 90 applies a correction voltage produced at the output of the sample and hold circuit 70 to the actuator 28 for one milli- second intervals so long as the separation between the trans ⁇ ducer 24 and the target track is less than 4.00 tracks and greater than 0.50 tracks.
  • the seek termination algorithm is accessed by the microprocessor 54 at a point where the correction for overshoot is made by reversing the direction that the transducer 24 moves.
  • FIGURES 14 through 17 show, in simplified form, the basic steps of the four major pertinent algorithms implemented in the microprocessor 54: track accumulator interrupt, long seek, seek termination, and short seek.
  • updated information on the radial separation between the transducer 24 and the .target track is provided by inter ⁇ rupting those algorithms to calculate an updated value for the separation between the transducer 24 and the target track whenever four frames of embedded servo information are detected by the transducer 24. This is indicated by the transfer flag ⁇ INTERRUPT" at 100 in FIGURE 14.
  • the transfer flag ⁇ INTERRUPT indicates that the transfer flag ⁇ INTERRUPT.
  • FIGURE 14 After the track identification number or coarse track input (CTI) is read by the microprocessor 54 at 102, it is determined at 104 whether the track identification number or CTI read is valid or not. Since each servo or data track generates at least one signal for each data frame and may generate two signals within only one of the four data frames per sector (in the case of a data track), any identification number or CTI read indicative of a variation from such a pattern is invalid.
  • a track iden ⁇ tification number is calculated by subtracting the radial distance travelled during the last sector ( STdDT) by the transducer 24 relative to the disc 22 from the last track identification number or coarse track input (LSTCTI) as indi ⁇ cated at 106 through 110 in FIGURE 14.
  • the microprocessor 54 saves this new coarse track input (NEW CTI) for future use.
  • the distance travelled during the previous sector interval (LSTdDT) is used, as shown at 112. If the coarse track input (CTI) is valid, it replaces the last coarse track input (LSTCTI) and is subtracted from it in order to calculate the new distance travelled between adja ⁇ cent sectors (dDT) as shown at 114 through 120 in FIGURE 14.
  • the newly acquired distance travelled between sectors (dDT) is used to update the distance between the trans ⁇ ducer 24 and the target track, i.e. the distance to travel (DTT) used by the microprocessor 54 in both the long and short seek algorithms, as will be described.
  • DTT distance to travel
  • the micro ⁇ processor 54 determines whether double prec s.-'on or single precision.arithmetic is to be used and updates the distance to travel (DDT) accordingly as indicated at 122 through 126 of FIGURE 14.
  • the faster single precision arithmetic is used when the distance between the transducer 24 and the target track is less than 16.00 tracks.
  • signals to the DAC 82 for adjusting the velocity with which the transducer 24 moves toward the target track are applied every eight sectors, i.e., after the transducer 24 has passed •over eight radial sectors 30 of servo information and the radial distance travelled during eight sectors intervals (d8DT) has been determined.
  • a sector counter is intially set at a value of eig and interrogated at 128. The counter is decremeted at 130 each time that the transducer 24 passes over a radial sector 30 until its count equals zero.
  • the microprocessor 54 After decrementing the sector counter, if necessary, the microprocessor 54 returns to the interrupted algorithm, as indicated by the transfer flag "RETURN FROM INTER ⁇ RUPT" at 132.
  • a command algorithm directs the microprocessor 54 to either the long seek or the short seek algorithm depending on the distance separating the transducer 24 from the target track. If the separation is less than 4.00 tracks, the micro ⁇ processor 54 uses the short seek algorithm, while if the distance is greater than or egual to 4.00 tracks, the microprocessor 54 uses the long seek algorithm.
  • FIGURES 15a and 15b A simplified flow diagram for the long seek algorithm is shown in FIGURES 15a and 15b.
  • the microprocessor 54 ascertains at 204 that there is currently valid sector data, i.e., that DTT has been updated and has not previously been read by the microprocessor 54 since being updated This determination, that there is valid sector data to be read, is made at various points in the algorithms and is indicated by the phrase "SECTOR" within a diamond block in the FIGURES, such as at 204 in FIGURE 15a.
  • the microprocessor 54 When microprocessor 54 has determined that there is valid sector data, the microprocessor 54 at 206 sets the vari ⁇ able, distance to travel for the current DAC calculation (DTTCDC), equal to the distance to travel (DTT) as has been determined by the microprocessor 54 using the track accumulator interrupt algorithm. The absolute value of this quantity is also deter ⁇ mined. Based on the absolute value of DTTCDC, a value VSN (velocity schedule normalized) related to the velocity with which it is desired to move the transducer 24 is chosen from a table programmed into the memory of the microprocessor 54, as shown at 208 through 218 of FIGURE 15a. This value is updated only after the transducer 24 has passed eight radial sectors of servo information.
  • DTTCDC vari ⁇ able, distance to travel for the current DAC calculation
  • VSN velocity schedule normalized
  • VSN is automatically chosen without reference to the programmed table.
  • the determination of whether the absolute value of DTTCDC is less than 16.00 tracks at 212 is made in order to ascertain whether single precision or double precision arithmetic should be used and to provide at appropriate points in the algorithms indications or so-called flags so that the microprocessor 54 uses the desired single or double precision arithmetic.
  • the microprocessor 54 derives the actual value of the signal to be applied to the DAC 82, VAN, from (1) the value for VSN, (2) the radial distance travelled by the transducer 24 during the previous eight sector intervals (d ⁇ DT) and (3) the velocity of the transducer 24 at the beginning of the eight sector interval (V1N).
  • the radial distance travelled during the previous eight sector intervals (d ⁇ DT) is calculated by sub ⁇ tracting the distance to travel for the current DAC calculation (DTTCDC) from the distance to travel for the last DAC calculation (DTTLDC). These operations are indicated at 220 through 232.
  • the microprocessor determines at 234 whether this is the first calculation being made in the long seek algorithm and proceeds accordingly. If it is the first calculation, the microprocessor 54, at 238 in FIGURE 15b, assures that the posi ⁇ tion switch 90, the DAC 1 switch 86 and the DAC 2 switch 92 27.
  • TGTTRK SEL target track
  • TR SEL transducer 24 to be used
  • the microprocessor 54 closes the DAC 1 switch 86, applying the analog voltage generated in the DAC 82 to the actuator 28 through the buffer amplifier 84 and the power ampli ⁇ fier 88.
  • the microprocessor 54 proceeds in the loop between 250 and 258 in FIGURE 15b for a maximum of eight sector intervals, i.e. , until the sector counter has been decremented from eight to zero, or until the absolute value of the radial separation between the transducer 24 and the target track (DTT) is less than 1.25 tracks, at which point in the latter case the micro ⁇ processor 54 accesses the seek termination algorithm.
  • the sector counter After the sector counter has been decremented to zero, it is reset back to eight at 260. If the separation between the transducer 24 and the target track is greater than 16.00 tracks, double precision arithmetic is used and the microprocessor 54 repeats the long seek algorithm beginning at 206 in FIGURE 15a in order to generate a new value of VAN to be applied to the DAC 82.
  • VAN VAN is generated as shown in the flow chart of FIGURE 15b between 264 and 278 in a manner similar to that used with respect to the calculation made using double precision arithmetic as pre ⁇ viously described and shown on the flow chart of FIGURE 15 between 216 and 230.
  • This new value of VAN is provided to the DAC 82 at 280 and the microprocessor 54 thereafter repeats the portion of the long seek algorithm indicated on the flow chart of FIGURE 15b between 250 and 258 as has been
  • the transducer 24 is moved toward the target track by means of the microprocessor 54 operating within the long seek algorithm and providing signals to the DAC 82 to change the velocity of the transducer 24 every eight sector intervals as it proceeds toward the target track until the distance to travel is less than 1.25 tracks, as determined at 256 on the flow chart in FIGURE 15b, at which point the microprocessor 54 accesses the seek termination algorithm.
  • the DAC 1 switch 86 is opened and the position switch 90 is closed.
  • the position switch 90 allows the comparison voltage appearing at the output of the sample and hold circuit 70 to be applied through the compen ⁇ satory amplifier circuit 94 and the power amplifier 88 to the actuator 28.
  • this analog voltage tends to move the transducer 24 toward the target track, which in turn decreases the voltage. This voltage is zero when in fact the transducer 24 is correctly positioned in alignment with the target track. The generation and characteristics of this analog voltage will be subsequently described in more detail.
  • a 3.2 millisecond timer is started. So long as the distance to travel (DTT) is less than 1.00 but greater than -1.00 tracks (a negative distance to travel indicates that the target track has been overshot by the transducer 24), the 3.2 millisecond timer will be allowed to time out. If this occurs, the seek has essentially been completed, i.e., the target track has been accessed and the final steps of the algorithm shown in the flow chart of FIGURE 16 at 320 through 330 are performed by the microprocessor 54.
  • DTT distance to travel
  • -1.00 tracks a negative distance to travel indicates that the target track has been overshot by the transducer 24
  • These steps involve setting as new initial values for a future seek the previous destina ⁇ tion value for the target track (INT TRK and DST TRK) and the transducer selection (INT TR and DST TR) and also deter ⁇ mining whether the transducer 24 is at a track greater than 29.
  • the current in the transducer 24 must be modified for a read/write operation.
  • the microprocessor 54 has indicated that the transducer 24 is within 1.00 tracks of the target track, the transducer 24 could still be moving slightly radially.
  • the final 5 millisecond time delay at 326 through 330 permits the transducer 24 to settle on the target track.
  • microprocessor 54 control over the radial position of the transducer 24 ceases.
  • the transducer 24 is maintained in correect alignment with the target track by the comparison voltage at the output of the sample and hold circuit 70 which is applied through the compensatory amplifier circuit 94, the position switch 90 and the power amplifier 88 to the actuator 28 as will be described.
  • the microprocessor 54 proceeds from 310 to 312 or from 314 to 316 in FIGURE 16 and causes signals to be generated for reversing the direction of motion of the transducer 24 and moving it at the maximum possible velocity. These signals are provided to the DAC 82, the position switch 90 opened and the DAC 2 switch 92 closed as indicated at 318.
  • the DAC 2 switch 92 functions similarly to the DAC 1 switch 86 except that a higher voltage is applied to the actuator 28 through the DAC 2 switch 92. This higher voltage is intended to overcome the mementum of the transducer 24 and reverse its direction of motion.
  • the absolute value of the distance separating the transducer 24 from the target track (DDT) is re-evaluated at 336. If this quantity is less than 4.00 tracks, the DAC 2 switch 92 is opened, the position switch 90 is closed, a 1 millisecond timer is started and the microprocessor 54 proceeds to a point within the short seek algorithm indicated by the transfer flag "WAIT 21" at 344, as will be discussed.
  • the microprocessor 54 at 340, prepares to return to the long seek algorithm, setting initial values on DTTLDC and V1N, resetting the sector counter to zero and resetting the 16.00 track indicators or flags used with respect to the selection of single or double precision arithmetic.
  • the DAC 2 switch 92 is opened, all signals are cleared from the DAC 82 and the DAC 1 switch 86 is closed before the microprocessor 54 returns to the long seek algorithm as indicated by the transfer flag "WAIT 30" at 346.
  • the short seek algorithm is accessed by the microprocessor 54 either as a result of an instruction to it during the com ⁇ mand algorithm or when the transducer 24 has overshot the target track by less than 4.00 tracks.
  • FIGURE 17 a flow chart of the major steps in the short seek algorithm is shown.
  • Blocks 402 through 414 indicate operations by the microprocessor 54 in the short seek algorithm that are similar to operations performed and already described by the micro ⁇ processor 54 in the long seek algorithm. Specifically, initial conditions are set and signals indicative of the particular transducer 24 and target track are outputted.
  • the short seek algorithm essentially modulates the posi ⁇ tion switch 90 open and closed so that the comparison voltage at the output of the sample and hold circuit 70 is periodically applied to the actuator 28 when the absolute value of the dis ⁇ tance to travel (DTT) remains less than 4.00 tracks and greater than 0.50 tracks.
  • the position switch 90 is closed and a 1 millisecond timer is started as indicated at 416. So long as the distance to travel (DTT) remains within the limits mentioned, the 1 millisecond timer is allowed to time out and the position switch 90 remains closed.
  • the position switch 90 is opened as indicated at 426 and simul ⁇ taneously, a 4 millisecond timer is started.
  • This timer is allowed to time out only if the absolute value of the distance to travel (DTT) remains within the range mentioned, i.e., greater than 0.50 tracks and less than or equal to 4.00 tracks. If in fact the 4 millisecond timer does time out, the position switch 90 is closed, once again applying the comparison voltage at the
  • OMPI IPO output of the sample and hold circuit 70 to the actuator 28 an ⁇ starting a 1 millisecond timer.
  • the microprocessor 54 returns to that part of the short seek algorithm which permits the 1 millisecond timer to time out so long as the absolute value of the distance to travel (DTT) remains within the indicated range.
  • the microprocessor 54 determines whether the dis ⁇ tance to travel is positive or negative and the appropriate point, 312 or 316, of the seek termination algorithm concerning overshoot is accessed by the microprocessor 54 as indicated by the transfer flags "GO FWD" and "GO REV" at 442 and 444 respec ⁇ tively.
  • the microprocessor 54 operates within that algorithm as has been previously described.
  • the timer is stopped (if it has been started), the posi ⁇ tion switch 90 is closed (if it is not closed) and the micropro- ce ⁇ sor 54 then accesses the seek termination algorithm at its initial point and proceeds through it as has been described.
  • the transducer 24 Once the transducer 24 has been placed into proximity with the selected track, the transducer 24 must be maintained in alignment with that track.
  • the same servo data, differently processed, is used for maintaining the transducer 24 in align ⁇ ment with the selected data track as was used to assist the transducer 24 in accessing the selected data track.
  • This main- tenence function is enhanced by the special encoding of the data frames which has been previously discussed.
  • position detector circuitry compares the amplitude of the pulse at the first location for servo infor ⁇ mation with the amplitude at the second location in one pre ⁇ selected data frame and provides feedback to reposition the transducer 24 as necessary.
  • This analog signal is provided at the output of the sample and hold circuit 70 and is applied to the actuator 28 through the compensatory amplifier circuit 94, the position switch 90 and the power amplifier 88.
  • the analog signal comparison is used not
  • the particular data frame in which the comparison is made by the position detector circuitry depends upon the se ⁇ lection of the data track with which it is desired to posi ⁇ tion the transducer 24 in alignment.
  • the data frame chosen for the comparison is that for which 'the servo tracks adjacent to the selected data track have recorded servo signals from the transducer 24 appearing at different locations within the data frame.
  • data track DT 4.0 is the selected data track, for example, data frame 0 is chosen for the comparison.
  • an electrical signal repre- ⁇ enting the selected data track is sent through the micro ⁇ processor unit and interface 54 to a target track decoder cir ⁇ cuit 80.
  • Detected synchronization signals from sync detector 56 are also sent through a data frame counter 64 to the target track decoder 80.
  • Time delayed synchronization signals repre- ⁇ enting times HI and H2 corresponding to the Gl and G2 locations for servo signals within the data frames are applied to the tar ⁇ get track decoder 80 from time delays 60 and 62 respectively.
  • target track decoder 80 produces a pair of output signals, each of which comprises a single pulse synchronized to the signal from the transducer 24.
  • each of the outputs Gl* and G2' from the target track decoder 80 comprises a single pulse precisely located with respect to the synchronization signals detected by the transducer 24 and produced at the output of the buffer 34.
  • the temporal locations of the Gl* and G2* pulses with respect to the synchronization signal detected by the transducer 24 and appearing at the output of the buffer 34 depends upon the target track selected.
  • the Gl' pulse occurs at the time corresponding to the first possible location within data frame 0 for a servo signal while the ⁇ 33 -
  • G2' pulse corresponds to the second possible location within data frame p for a servo signal since for data frame 0, the servo tracks adjacent to data track DT 4.0 have servo signals differently located for this data frame, as can be seen with reference to FIGURE 8.
  • the pulses are applied to peak detect and hold cir ⁇ cuits 66 and 68, the inputs of which receive the buffered signal from the transducer 24.
  • the Gl' pulse gates the peak detect and hold circuit 66 at a time corresponding to the first possible location for a servo signal in data frame 0, so that the peak of a signal from the transducer 24 occurring at such a time will be detected and held in circuit 66.
  • the G2' pulse gates the peak detect and hold cir ⁇ cuit 68 at a time corresponding to the second possible location for a servo signal in data frame 0 so that a detected servo signal from data frame 0 occurring at a time corresponding to such location will have its peak detected and held in cir ⁇ cuit 68.
  • Sample and hold circuit 70 produces an output indica ⁇ tive of the difference between these peaks. This output will be zero when the transducer 24 is aligned with data track DT 4.0, and will be po ⁇ itive or negative if the transducer 24 drifts away from alignment with that data track.
  • the Gl' and G2' pulses from the target track decoder 80 will be reversed, i.e., the Gl* pulse will occur at a time corresponding to the second possible location for servo information in data frame 0 while the G2* pulse will occur at a time corresponding to the first possible location for servo information in data frame 0.
  • the output of the sample and hold circuit 70 will then be zero if the transducer 24 maintains its alignment with data track DT 0.0 and will have a non-zero value if the transducer 24 drifts out of alignment with that data track.
  • This output voltage is used to provide a feedback signal to the actuator 28 which moves the carriage to radially adjust the position of the transducer 24.
  • the compensatory amplifier circuit 94 provides high and low frequency compensation for this analog signal which is applied through the position switch 90 and the power amplifer 88 to the actuator 28 in order to cause the actuator 28 to move the carriage 26 so that the transducer 24 is moved back into alignment with data track DT 4.0.
  • the output of sample and hold circuit 70 is digitized by fine position digitize 72 and inputted to the microprocessor 54. If a data track other than data tracks DT 0.0 or DT
  • the output pulses from the target track decoder 80, Gl* and G2' will correspond to the first and second possible locations for servo information sig ⁇ nals in other data frames.
  • the Gl* and G2* pulses correspond to the locations of the first and second possible locations for servo information signals in data frame 2, as can be determined by reference to FIGURE 8.
  • the detected signal pulses from the transducer 24 corresponding to the first and second locations within data frame DT 0.0 are equal so that the comparison results in a zero differ ⁇ ence voltage and output.
  • the difference voltage decreases since the pulse at the Gl location increases in amplitude while the pulse at the G2 location decreases in amplitude.
  • the voltage reaches a maximum negative value when the trans ⁇ ducer 24 is positioned over servo track ST 4.5.
  • the output voltage increases reaching a maximum positive value when the transducer 24 is positioned radially in alignment with servo track ST 3.5.
  • the output voltage is zero when the transducer 24 is aligned with data track DT 0.0 and data track DT 0.0" as well a ⁇ data track DT 4.0.
  • the slope of the voltage curve is opposite when the transducer 24 is aligned with the data track DT 0.0 and DT 0.0" to what it is
  • an error signal i.e., a positive or negative voltage at the output
  • the data tracks DT 4.0* and DT 4.0" located in the groups on either side are the nearest stable nulls, i.e., positions at which the error signal is zero and the slope of the voltage is in a direction tending to align the transducer 24 to the data track.
  • the data frame 0 is still used for the comparison of amplitudes of servo infor ⁇ mation signals.
  • the signals for the comparison are reversed, as has been described, in order that the slope of the output voltage curve be in the proper direction, as shown in FIGURE 12, to provide the required feedback voltage.
  • the distance between the stable nulls is a result of the specific encoding chosen for the servo tracks within a radial sector. If the Gray code were used, the positioning of the servo information signals encoded onto the servo tracks could vary between the first and second locations within the data frames of adjacent tracks with greater frequency, thus resulting in the stable nulls being positioned radially closer together. With the preferred method of encoding, however, the same encoding is used in the data frames of four adjacent tracks before the opposite encoding i ⁇ used for that data frame for the next four adjacent track ⁇ . There is thus less of a chance, with the preferred embodiment, that the transducer 24 will be erroneously maintained in alignment with a non- selected data track.
  • the microprocessor 54 Since the same encoding appears on a track in each group of track ⁇ , it i ⁇ necessary to monitor which of the similarly encoded tracks from the various groups the transducer 24 i ⁇ aligned with. Thi ⁇ can be accomplished by the microprocessor 54 accumulating the track identification numbers. The ability of the microprocessor 54 to keep an accurate count of the actual track numbers depends upon the radial rate of motion of the transducer 24 relative to the disc 22. The maximum permissible rate of motion of the transducer 24 in order to permit accumulation by the microprocessor 54 will depend upon the rate of rotation of the disc 22, the number of radial sec ⁇ tors 30 of servo information on the disc 22 and the number of data frames per track in each radial sector 30.
  • the fractional track detection which is made possible by the present invention is achieved whether or not the specific method of encoding presently preferred i ⁇ used or if another encoding, such as the Gray code i ⁇ u ⁇ ed, although the separa ⁇ tion of stable nulls would be decreased if some other encoding were used.
  • the pre ⁇ ent invention make ⁇ u ⁇ e of tribit encoding becau ⁇ e thi ⁇ encoding advantageously pro ⁇ vides synchronization signals along with servo information signals within each data frame.
  • many other methods make ⁇ u ⁇ e of tribit encoding becau ⁇ e thi ⁇ encoding advantageously pro ⁇ vides synchronization signals along with servo information signals within each data frame.
  • OMPI of encoding such as the uni-polar dibit could be used in the present invention and the same results in terms of frac ⁇ tional track detection and position detector stability would still be achieved.
  • the claims not be limited to the specific preferred embodiment discussed herein.

Landscapes

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

Abstract

Système et procédé permettant de positionner avec précision un organe transducteur (24) en alignement radial avec une piste de données sélectionnée sur un disque magnétique (22) en utilisant une commande par microprocesseur (54) et permettant de sauvegarder son alignement axial. Des servo-pistes divisées en secteurs (30), entremêlées radialement avec des pistes de données sur un disque magnétique, sont codées d'une manière unique à l'intérieur de groupes, le code comprenant l'emplacement des servo-signaux enregistrés à une première ou à une deuxième position à l'intérieur d'une pluralité de blocs de données situés sur les servo-pistes. Les servo-signaux enregistrés sont détectés par un transducteur (24) et comparés à une tension continue dans un comparateur (44) afin de produire une série d'impulsions d'horloge pour un registre à décalage (46). Une séquence prédéterminée d'impulsions correspondant aux emplacements possibles pour les servo-signaux enregistrés à l'intérieur du bloc de données dans un secteur (30) constitue la sortie de données vers le registre à décalage (46). La sortie du registre à décalage (46) est un nombre binaire correspondant à la servo-piste ou à la piste de données avec laquelle l'organe transducteur (24) est aligné radialement. Ces informations sont traitées pour identifier l'emplacement radial de l'organe transducteur (24). Un microprocesseur (54) détermine à partir de ces informations la séparation radiale entre l'organe transducteur (24) et la piste de données sélectionnées et produit en cas de besoin un signal provoquant le déplacement radial du transducteur (24).
PCT/US1982/000683 1981-10-22 1982-05-17 Procede et dispositif de positionnement d'un transducteur utilisant un codage de servo-piste noyee et une commande par microprocesseur WO1983001531A1 (fr)

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US313,655811022 1981-10-22

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1990005361A1 (fr) * 1987-03-02 1990-05-17 Unisys Corporation Systeme de servocommande pour unite de disques
WO1994012977A1 (fr) * 1992-11-30 1994-06-09 Samsung Electronics Co., Ltd. Circuit de lecture de donnees d'un disque

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3821804A (en) * 1972-01-19 1974-06-28 T Stevenson Servo system for positioning data transducer
US4149201A (en) * 1977-10-31 1979-04-10 Burroughs Corporation Transducer centering system
US4419199A (en) * 1981-05-09 1983-12-06 Occidental Chemical Corporation Process for phosphatizing metals

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3821804A (en) * 1972-01-19 1974-06-28 T Stevenson Servo system for positioning data transducer
US4149201A (en) * 1977-10-31 1979-04-10 Burroughs Corporation Transducer centering system
US4149200A (en) * 1977-10-31 1979-04-10 Burroughs Corporation Transducer positioning system
US4419199A (en) * 1981-05-09 1983-12-06 Occidental Chemical Corporation Process for phosphatizing metals

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1990005361A1 (fr) * 1987-03-02 1990-05-17 Unisys Corporation Systeme de servocommande pour unite de disques
WO1994012977A1 (fr) * 1992-11-30 1994-06-09 Samsung Electronics Co., Ltd. Circuit de lecture de donnees d'un disque
GB2278009A (en) * 1992-11-30 1994-11-16 Samsung Electronics Co Ltd Disk read-out circuit
AU666152B2 (en) * 1992-11-30 1996-02-01 Samsung Electronics Co., Ltd. Disk read-out circuit
GB2278009B (en) * 1992-11-30 1996-08-07 Samsung Electronics Co Ltd Disk read-out circuit

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