Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B21/00—Head arrangements not specific to the method of recording or reproducing
  • G11B21/02—Driving or moving of heads
  • G11B21/08—Track changing or selecting during transducing operation
  • G11B21/081—Access to indexed tracks or parts of continuous track
  • G11B21/083—Access to indexed tracks or parts of continuous track on discs
  • G11B21/085—Access to indexed tracks or parts of continuous track on discs with track following of accessed part
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B27/00—Editing; Indexing; Addressing; Timing or synchronising; Monitoring; Measuring tape travel
  • G11B27/10—Indexing; Addressing; Timing or synchronising; Measuring tape travel
  • G11B27/19—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier
  • G11B27/28—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier by using information signals recorded by the same method as the main recording
  • G11B27/32—Indexing; Addressing; Timing or synchronising; Measuring tape travel by using information detectable on the record carrier by using information signals recorded by the same method as the main recording on separate auxiliary tracks of the same or an auxiliary record carrier
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
  • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
  • G11B7/085—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam into, or out of, its operative position or across tracks, otherwise than during the transducing operation, e.g. for adjustment or preliminary positioning or track change or selection
  • G11B7/08505—Methods for track change, selection or preliminary positioning by moving the head

Definitions

• This invention relates to a system for sensing the rotational position of a rotating disk. More particularly, the invention relates to a system and method for placing sector marks on a rotating disk having coarse seek tracks in a manner that saves space on the disk and that eliminates the need for a special sector mark detector.
• a disk storage system regardless of whether such a system is a magnetic disk or an optical disk, data is written on or read from the disk surface as the disk rotates past read/write heads (the term "head" will be used in this disclosure to describe the device which senses the data during a read operation or causes the data to be written during a write operation).
• Data is typically recorded on the disk in concentric rings called tracks. Each track is advantageously divided into a number of segments called sectors. Such sectors provide an identifiable area on the disk where data may be stored and indexed for future retrieval.
• the head Before a read or write operation can be initiated, the head must be positioned over the desired track, and the disk must be rotated until the desired sector of the selected track is positioned under the head.
• the read/write heads are positioned at the correct track by means of a servo system.
• head positioning servo systems There are many types of head positioning servo systems known in the art, anyone of which could be used with the present invention.
• Another method places sector information with the regular data to be stored by the system.
• This approach divides the disk into sectors of a fixed size and writes a sector number at the beginning of each sector when the disk is formatted before data is written thereon.
• This method has the advantage of allowing the same read head to be used to read both the sector information and the data that is later written in the sector; but it has the disadvantage of using some of the sector space for the sector number (thereby decreasing data storage capacity), and it requires the use of special decoding circuitry to decode the sector number that is read, as well as to compare it with the desired sector number.
• the index mark is a unique type of sector mark that is used to mark the zero degree point of rotation.
• each sector is marked by the absence of data, i.e., a data gap, at a fixed rotational position from the index mark.
• this system merely counts the gaps from the index mark as the disk rotates to determine a desired sector location.
• the sector count is unfortunately lost when the head is moved to a new track until such time as the index mark again passes under the head.
• this approach slows down the operation of the disk storage system since more than one revolution may be required before the desired sector can be found.
• At least two coarse seek tracks will lie under the coarse track read head.
• the sector marks included in each coarse seek track divide the disk into equal sectors.
• the coarse track head means used to follow the coarse seek track senses the sector marks and, in cooperation with appropriate detection circuitry, generates an output signal indicating when each sector begins and ends. Because the disk rotates at a constant speed, and because each sector is equal, in size, this output signal assumes a fixed frequency, the period of which corresponds to the time it takes one sector to pass underneath the coarse track read head.
• phase lock loop techniques an oscillator is locked onto this output signal.
• a counter is then used to count the cycles of the oscillator.
• index mark representing a zero degree reference point for the rotating disk, is also sensed fay the coarse track read head for each revolution of the disk. This index mark, when sensed, is used to reset the counter.
• the counter always contains a count therein indicative of the rotational position (sector location) of the disk, regardless of whether the data read/write heads are moved from one track to another.
• FIG. 1 is a simplified top plan view of an information disk showing some of the coarse seek tracks located thereon;
• FIG. 2 is a diagramatic representation illustrating the system of the present invention wherein sector marks are selectively placed in the coarse seek tracks of FIG. 1;
• FIG. 3 is a block diagram of the present invention, including detection circuitry that could be used to detect and decode the sector marks placed in the coarse seek tracks of an information disk in accordance with the present invention.
• FIG. 1 is a simplified top plan view of an information disk 10 that, when inserted in an appropriate disk storage system, is rotated about its center 16.
• On the disk 10 are a plurality of coarse seek tracks 11-15, represented in FIG. 1 as concentric circles. (although only five coarse seek tracks are shown in FIG. 1, it is to be understood that any number of such tracks could be used.)
• the primary function of the coarse seek tracks 11-15 is to provide radial position information to the servo system.
• a servo system employing such coarse seek tracks is disclosed in application Serial No. 438,133, filed 11/1/82, "Fine and Coarse Servo System For Access and Tracking On An Optical Disk," assigned to the same assignee as is this application.
• the coarse seek tracks 11-15 are selectively spaced about the center 16 of the disk. Data is written on and read from a multiplicity of data tracks, not shown in the figure, located in the region or band 19 between the coarse seek tracks. Numerous fine servo systems could be employed in order to access a given data track once the region or band 19 has been accessed by a coarse servo system. Further, numerous coarse servo systems could be employed. For the description that follows, however, the preferred embodiment will be described in connection with the fine and coarse servo system described in the aforecited patent application, Serial No. 438,133, which application is incorporated by reference herein. This preferred servo system is designed for use with an optical disk, and so the description that follows will likewise be explained in terms of an optical disk. However, it is to be understood that the present invention could be used equally as well with magnetic or other information disk storage systems.
• a light source is used to project an elongated spot 17 or 18 on the surface of the disk 10.
• This elongated spot is reflected to a linear detector which can detect the position of the light spot on one or more of the coarse seek tracks.
• the length of the elongated spot of light is slightly longer than two data bands 19, and therefore covers two or three coarse seek tracks.
• Two different representations of the elongated light spot are included in FIG. 1.
• the light spot 17 is shown impinging on three coarse seek bands, while the light spot 18 is only impinging on two coarse seek bands.
• the spot 18 is the normal position of the spot during a read/write operation.
• FIG. 2 is a diagramatic representation illustrating how the system of the present invention divides two representative coarse seek bands 54-55 into sectors.
• Lines 40-51 are shown emanating from the center of the disk 16 to divide the coarse bands 54-55 into a multiplicity of sectors.
• the lines 40-51 are shown only for illustrative purposes and do not actually exist on the disk surface.
• the two coarse seek tracks 54-55, and all the other coarse seek tracks on the disk but not shown in the figure, are divided into a multiplicity of sectors represented in the figure as 20-29. Each sector spans the same number of degrees and all gaps between sectors are equal.
• An index mark 30 is a unique sector mark indicating the zero degree reference point of rotation.
• the sectors are actually formed by writing the coarse seek track an appropriate number of degrees, stopping or altering the writing for the appropriate number of degrees to form a gap between the sectors, and repeating this process until all sectors of the band are written.
• the signal used to write the coarse seek track may be continuously on for the duration of the sector, and modulated 50% on and 50% off in the gap between sectors.
• All coarse seek bands are written by a special servo writing machine such that the sector marks are precisely aligned.
• each sector may be .022 degrees in length, with a gap between sectors of .022 degrees.
• phase of the clock an appropriate amount (such as 90 or 180 degrees) in the gap between sectors, rather than physically leaving a gap in the coarse servo track or altering the modulation scheme of the signal used to write the coarse servo track.
• phase change could be easily detected to mark the beginning or end of each sector, and would still provide a continuous clock source for other purposes.
• the sector information is contained within the servo tracks, and as such, no additional disk surface area is required to include this sector information on the disk.
• FIG. 3 is a simplified block diagram showing the principal components of the present invention, including how the sector marks may be detected.
• Light 59 reflected off the surface of the disk 10, impinges on a linear detector 60.
• the reflected light 59 originates from a light source 58, such as a laser, which light source directs incident light 58' (represented as a dashed line in FIG. 3) to the disk 10 so as to form an elongated spot 17 or 18 (FIG. 1) thereon.
• the incident and reflected lights are directed to and from the disk 10 through a head assembly 57 mounted to a movable carriage 56.
• Suitable optic elements (lenses, mirrors, etc.) are, of course, used to direct the incident and reflected light along the desired paths.
• the carriage 56 is radially positioned with regard to the disk 10 under control of the servo system.
• the linear detector 60 has two outputs 61 and 62. These outputs have a signal that is proportional to the amount and position of light impinging on their respective half of the linear detector.
• the reflected light 59 varies in intensity as it passes over the sector marks in the coarse seek bands. This variation in intensity occurs at a position along the length of the light spot corresponding to the relative position of the coarse seek tracks within this elongated light spot.
• the output signals 61, 62 vary as a function of the relative position and content (off or on) of the reflected light 59 that strikes the detector 60. As such, these signals will typically have a frequency associated therewith that is a function of the rotational speed of the disk and the sector gap and length, and an amplitude that is a function of the relative position of the servo tracks within the elongated spot.
• Low pass filters 63, 64 and band pass filters 65, 66 are used to filter the outputs of the linear detector 60. These outputs will vary in sinusoidal fashion as the disk rotates and as the sector gaps are encountered. This sinusoidal waveform is supplied to each of the inputs of a summing amplifier 67. The polarity associated with the inputs to the amplifier 67 is such that the amplifier 67 subtracts the two signals and supplies the result to the servo system. The servo system responds to this signal by moving the light spot until it is centered on the desired coarse seek band. When this occurs, the two outputs of the linear detector 60 will be equal, the two inputs to the amplifier 67 will be equal, and the signal to the servo controller will be zero. Further details relative to the operation of the light spot, linear detector, and servo system may be found in the previously referenced copending patent application, Serial No. 438, 133.
• the outputs of the two band pass filters 65, 66 are also combined in a functional OR circuit 68. Since the reflected light spot 59 is always over at least one coarse seek track, at least one of the inputs to the OR circuit 68 will have a sine wave applied to it corresponding to the frequency generated by the light spot as the sector marks rotate by it.
• the output of the OR circuit 68 is applied to the input of a phase lock loop oscillator 69, which oscillator will not pass the irregularity in the sine wave caused by the index mark 30 (see FIG. 2).
• the output of the phase lock loop oscillator is connected to a counter 70 and to an index decoder 71.
• the output of the OR circuit 68 is also applied to the index decoder 71.
• the counter 70 is incremented by the output of the phase lock loop oscillator 69.
• the frequency of the oscillator 69 is, in turn, locked to the rate at which the sector marks (gaps) pass through the light spot. This frequency may be directly related to the sector count or an integer multiple of the sector count. In either event, the counter is configured so as to maintain a running count of the sector count as the disk rotates, even when the servo is moving the light spot while seeking a different track.
• the index decoder 71 uses techniques that are well known to those skilled in the art of logic design, compares the output waveform of the OR circuit 68, which includes the irregularity of the index mark, to the output of the phase lock loop oscillator, which does not include the irregularity of the index mark. When the index mark is detected, the index decoder 71 generates an output signal which clears the counter 70, and the running count of the sector number starts over. Thus, the count held in the counter 70 is always synchronized with the index mark, and the count thus indicates the rotational position of the disk by indicating the number of sector locations from the index mark that the disk has rotated.

Landscapes

• Signal Processing For Digital Recording And Reproducing (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=23875503

Family Applications (1)

Country Status (3)

Families Citing this family (4)

Family Cites Families (9)

• 1984
  • 1984-03-05 EP EP19840901476 patent/EP0138947A1/de not_active Withdrawn
  • 1984-03-05 WO PCT/US1984/000339 patent/WO1984003583A1/en not_active Ceased
  • 1984-03-06 CA CA000448976A patent/CA1213977A/en not_active Expired

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events