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Method and apparatus for positioning a transducer using embedded servo track encoding
| Details |
Inventors: Nalley, Robert E.; Shenfield, Leonard R.;
Assignee: Disctron, Inc. (Milpitas, CA)
Primary Examiner: Eddleman; Alfred H.
Assistant Examiner: Wong; Kin
Attorney, Agent or Firm: Spensley, Horn, Jubas & Lubitz
A system and method for accurately positioning a transducer means radially in alignment with a selected data track on a magnetic disc and maintaining it in radially alignment is described. Sectored servo tracks radially interspersed with data tracks on a magnetic disc, are uniquely encoded within groups, the code comprising the location of recorded servo signals at either a first or second position within a plurality of data frames located on the servo tracks. The recorded servo signals are detected by a transducer and compared with a D.C. voltage in a comparator in order to produce a series of clock pulses for a shift register. A predetermined sequence of pulses corresponding to possible locations for recorded servo signals within the data frame in a sector is the data input to the shift register. The output of the shift register is a binary number corresponding to the servo track or the data track with which the transducer is radially aligned. This information is processed to identify the radial location of the transducer and to provide, if required, a signal to move the transducer radially. The use of a unique encoding scheme wherein the encoding on the successively positioned servo tracks for any data frame is allowed to change only once every N number of tracks, where N is the number of data frames per track, enhances the abiity of a second position detecting means to maintain the transducer in radial alignment with the selected data track. This is accomplished by circuitry which compares the peaks of the signals corresponding to the first and second locations within a selected data frame, the selection of the data frame depending upon the selected data track, and applying the signal to move the transducer radially, if necessary. |
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DETAILED DESCRIPTION In the present invention, all the servo information necessary for both the track accessing and track following functions is combined and encoded in one sequence on the servo tracks of a magnetic disc.
Importantly, the decoding scheme of the present invention allows for track identification to the nearest servo or data track, i.
e.
, with a resolution of one-half of a track since the servo and data tracks are interspersed, the data tracks being located halfway between adjacent servo tracks.
Furthermore 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.
In order to achieve the objects of fractional track detection, high stability and the use of a minimum amount of disc space in order to provide servo information to enable a transducer positioning mechanism to access a selected track and to accurately follow that track while the disc is rotating, 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 uniquely 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 provides servo information at either a first or second location within the data frame.
The preferred embodiment described herein also provides an additional recorded magnetic transition at the beginning of each data frame as a synchronization signal.
The data tracks are located outside the narrow radial sectors and have radial locations equidistant between those of the servo tracks, i
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