US 5,050,018 A · Apparatus and method for reading helically recorded tracks and rereading tracks as necessary

Abstract

A helical drive system (10) reads tracks (18) on a storage medium (12), including tracks which appear as distorted tracks. Each track (18) comprises a plurality of blocks of data, with each block having unique block-identifying information. A track-following servo system (84) causes a read head (16C) to traverse predetermined original azimuthal paths (P0) across the storage medium (12) for reading the blocks recorded along each of the original azimuthal paths (P0). A controller (50) uses the block-identifying information to determine whether any blocks expected to be read during the traversal of the original azimuthal paths (P0) were not read. If expected blocks were not read, the controller (50) repositions the storage medium (12) and directs that the medium (12) be re-read with the head (16C) positionally offset until the expected blocks are actually read. During the re-read attempts, the read head (16C) is positionally offset to traverse sets of modified azimuthal paths (P1, P2, P3, . . . P10 ). Each set of modified azimuthal paths (P2, P3, . . . P10) is offset with respect to the original azimuthal paths (P0) relative to a direction of medium travel (15), thereby providing opportunities to read blocks which would not otherwise be read due to distortion of the tracks (18). In one mode of the invention, the controller (50) dynamically selects from among a plurality of offset degree values based on the historical success rate of the differing offsets in reading blocks which formerly were missing blocks.

Claims34

Dependent claims

means for transporting said storage medium in a direction of medium travel;
a rotatable drum having a portion of a peripheral surface thereof contiguous with said storage medium as said storage medium is transported therepast by said transporting means;
reading means mounted on said drum for traversing original azimuthal paths across said storage medium and for reading blocks including said block-identifying information recorded along at least a portion of each of said original azimuthal paths;
control means for using said block-identifying information to determine whether any blocks expected to be read during the traversal of said original azimuthal paths were not read and for generating a signal in accordance with said determination;
and,
repositioning means mounted on said drum and responsive to said signal generated by said control means for repositioning said reading means whereby said reading means traverses modified azimuthal paths in an attempt to read a block which should have been previously read but was not previously read, said modified azimuthal paths being offset with respect to said original azimuthal paths relative to said direction of medium travel.

3 more elements

A method for reading information recorded on a storage medium in helical tracks, with each track comprising a plurality of blocks of data with each block having unique block-identifying information, said method comprising:

transporting said storage medium in a direction of medium travel past a rotatable drum, said rotatable drum having a portion of a peripheral surface thereof contiguous with said storage medium as said storage medium is transported therepast;
rotating said rotatable drum whereby reading means mounted on said drum traverses original azimuthal paths across said storage medium;
reading blocks including said block-identifying information recorded along at least a portion of each of said original azimuthal paths;
using said block-identifying information to determine whether any blocks expected to be read during the traversal of said original azimuthal paths were not read;
and,
repositioning, in response to said determination, said reading means whereby said reading means traverses a set of modified azimuthal paths in an attempt to read a block which should have been previously read but was not previously read, said set of modified azimuthal paths being related to said original azimuthal paths relative to said direction of medium travel.

3 more elements

Apparatus for reading information recorded on a storage medium in helical tracks, with each track comprising a plurality of blocks of data with each block having unique block-identifying information, said apparatus including means for transporting said storage medium in a read direction and in a backward direction opposite to said read direction;

a rotatable drum having a portion of a peripheral surface thereof contiguous with said storage medium as said storage medium is transported therepast by said transporting means;
reading means mounted on said drum for traversing a set of original azimuthal paths across said storage medium and for attempting to read blocks including said block-identifying information recorded along at least a portion of each of said original azimuthal paths;
and, positioning means mounted on said drum for selectively repositioning said reading means;
wherein the improvement comprises:
control means for using said block-identifying information to determine whether any blocks expected to be read during the traversal of said set of original azimuthal paths were not read and therefore are missing blocks;
for directing said transporting means to transport said storage medium a predetermined distance in said backward direction upon the determination that blocks are missing;
for applying a signal in accordance with said determination to said positioning means whereby, as a portion of said storage medium is re-read in attempt to read missing blocks, said reading means can traverse a first set of modified azimuthal paths, with each of said modified azimuthal paths of said first set being offset by a first offset degree from its corresponding original azimuthal path;
for determining whether all missing blocks were read by said reading means traversing said first set of modified azimuthal paths;
and, for directing continued reading of said storage medium with said reading means at said first offset degree if all of said missing blocks were read as reading means traversed said first set of modified azimuthal paths.

6 more elements

(1) transporting said storage medium in a read direction past a rotatable drum, said rotatable drum having a portion of a peripheral surface thereof contiguous with said storage medium as said storage medium is transported therepast;
(2) rotating said rotatable drum whereby reading means mounted on said drum traverses original azimuthal paths across said storage medium;
(3) reading blocks including said block-identifying information recorded along at least a portion of each of said original azimuthal paths;
(4) using said block-identifying information from blocks read during step (3) to determine whether any blocks expected to be read during the traversal of said original azimuthal paths were not read and therefore are missing blocks;
(5) transporting said storage medium a predetermined distance in a direction which is the reverse of said read direction;
(6) using said determination of step (4) to cause said reading means to traverse a first set of modified azimuthal paths offset by a first offset degree from said original azimuthal paths, said first modified azimuthal paths being offset with respect to said original azimuth paths relative to said direction of medium travel;
(7) reading blocks including said block-identifying information recorded along at least a portion of each of said modified azimuthal paths included in said first set of modified azimuthal paths;
(8) using said block-identifying information from blocks read during step (7) to determine whether any blocks expected to have already been read were not read and therefore are still missing blocks;
(9) continuing to read said storage medium with said reading means at said first offset degree if it were determined at step (8) that all of said missing blocks were read as reading means traversed said first set of modified azimuthal paths.

6 more elements

a rotatable drum having a portion of a peripheral surface thereof contiguous with said storage medium as said storage medium is transported therepast by said transporting means;
reading means mounted on said drum for traversing original azimuthal paths across said storage medium and for attempting to read blocks including said block-identifying information recorded along at least a portion of each of said original azimuthal paths;
and, positioning means mounted on said drum for selectively repositioning said reading means;
wherein the improvement comprises:
control means for using said block-identifying information to determine whether any blocks expected to be read during the traversal of said original azimuthal paths were not read and therefore are missing blocks;
for directing said transporting means to transport said storage medium a predetermined distance in said backward direction upon the determination that blocks are missing;
for using information derived from said block-identifying information to select from a plurality of potential offset positions for said reading means whereby for each offset position said reading means traverses unique sets of modified azimuthal paths in an attempt to re-read missing blocks, said offset positions of differing sets being separated by a unique offset distance from said original azimuthal paths relative to said direction of medium travel.

4 more elements

(1) transporting said storage medium in a read direction past a rotatable drum, said rotatable drum having a portion of a peripheral surface thereof contiguous with said storage medium as said storage medium is transported therepast;
(2) rotating said rotatable drum whereby reading means mounted on said drum traverses original azimuthal paths across said storage medium;
(3) reading blocks including said block-identifying information recorded along at least a portion of each of said original azimuthal paths;
(4) using said block-identifying information from blocks read during step (3) to determine whether any blocks expected to be read during the traversal of said original azimuthal paths were not read and therefore are missing blocks;
(5) transporting said storage medium a predetermined distance in a direction which is the reverse of said read direction;
(6) using information derived from said block-identifying information to select from a plurality of potential offset positions for said reading means;
and,
(7) repositioning said reading means at said selected offset position whereby said reading means traverses a set of modified azimuthal paths in an attempt to re-read missing blocks.

5 more elements

Dependencies are inferred from the claim text.

Apparatus and method for reading helically recorded tracks and rereading tracks as necessary

Life of this patent

Apparatus and method for reading helically recorded tracks and rereading tracks as necessary

Life of this patent

Abstract

Claims34