G - Physics – 11 – B
Patent
G - Physics
11
B
318/93
G11B 27/32 (2006.01) G11B 27/13 (2006.01)
Patent
CA 1180050
ABSTRACT. A method of, and apparatus for, generating a unique index mark from the commutation signal of a d.c. brushless motor. A unique index mark is provided to avoid errors in addressing a memory location on a disk surface by corre- lating the commutation signal from a d.c. motor with a synchronising signal present on one or more discrete tracks of the disk. The proportion of the synchronising signals on one track depends on the number of phases of the d.c. motor although typically with a 2-phase motor one-half of the track contains the synchronising signal, the other half of the track being erased. The commutation signals and the synchronising signals are correlated using a microprocesser and a flip-flop. A sensing head looks for a synchronising signal which is typically 10 individual data blocks of short duration. The detected blocks are counted in each half revolution of the disk, timed from the index edge and comparing the counts in successive half-revolutions in a comparator over several disk revolutions. The microprocesser then identifies from the comparator output the half-revolution of the disk in which the synchronising signal was recorded. The microprocesser receives the output of the comparator and forces the output of the flip-flop hi setting an initial condition. Thereafter the microprocesser ensures that the flip-flop output is always correlated with the synchronising signal thereby producing a unique index mark.
406243
Ruxton David S.
Stewart Alec D.
Fetherstonhaugh & Co.
Rodime Limited
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