EP0091441A1 - 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

Info

Publication number
EP0091441A1
EP0091441A1 EP19820902215 EP82902215A EP0091441A1 EP 0091441 A1 EP0091441 A1 EP 0091441A1 EP 19820902215 EP19820902215 EP 19820902215 EP 82902215 A EP82902215 A EP 82902215A EP 0091441 A1 EP0091441 A1 EP 0091441A1
Authority
EP
European Patent Office
Prior art keywords
servo
transducer
track
data
tracks
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19820902215
Other languages
German (de)
English (en)
Inventor
Robert E. Nalley
Leonard R. Shenfield
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
DATA PERIPHERALS
Original Assignee
DATA PERIPHERALS
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 DATA PERIPHERALS filed Critical DATA PERIPHERALS
Publication of EP0091441A1 publication Critical patent/EP0091441A1/fr
Withdrawn legal-status Critical Current

Links

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 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.
  • 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.
  • 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 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.
  • 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 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 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.
  • 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.
  • 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 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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 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 (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 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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 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 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.
  • 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.
  • 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 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 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 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).
EP19820902215 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 Withdrawn EP0091441A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US31365581A 1981-10-22 1981-10-22
US313655 1981-10-22

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EP0091441A1 true EP0091441A1 (fr) 1983-10-19

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EP19820902215 Withdrawn EP0091441A1 (fr) 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

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WO (1) WO1983001531A1 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4808900A (en) * 1987-03-02 1989-02-28 Unisys Corp. Bi-directional difference counter
JPH07503571A (ja) * 1992-11-30 1995-04-13 三星電子株式会社 ディスク読み出し回路

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Publication number Priority date Publication date Assignee Title
GB1369155A (en) * 1972-01-19 1974-10-02 Int Computers Ltd Servo systems
US4149200A (en) * 1977-10-31 1979-04-10 Burroughs Corporation Transducer positioning system
DE3118375A1 (de) * 1981-05-09 1982-11-25 Metallgesellschaft Ag, 6000 Frankfurt Verfahren zur phosphatierung von metallen sowie dessen anwendung zur vorbehandlung fuer die elektrotauchlackierung

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8301531A1 *

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