Patent ID: 6470291
Filing Date: 2002-10-22
Classification: G11B

Abstract:
A rotational velocity measurement method, comprising:generating a predetermined number of tachometer pulses during each revolution of a shaft driven by a motor; sampling for tachometer pulses at a constant predetermined sampling rate; if there are a plurality of tachometer pulses within each sample interval: a) measuring a delay between a last tachometer pulse detected before the start of one sample interval and the start of the one sample interval; b) counting one or more tachometer pulses during the one sample interval; c) measuring a delay between a last tachometer pulse detected during the one sample interval and the end of the one sample interval; and d) calculating a first value related to rotational shaft velocity from the pulse count and the difference between the delays measured in substeps (a) and (c); and if there are not a plurality of tachometer pulses within each sample interval: 1) measuring a delay between a first tachometer pulse and the start of a next subsequent sample interval; 2) counting one or more sample intervals extending through detection of a second tachometer pulse; 3) measuring a delay between the second tachometer pulse and the start of a next subsequent sample interval; and 4) calculating a second value related to rotational shaft velocity from the interval count and the difference between the delays measured in substeps (1) and (3), wherein: the first value comprises a ratio of the pulse count to the sum of the sample interval and the difference between the delays measured in substeps (a) and (c); and the second value comprises the inverse of the sum of the sample interval count and the difference between the delays measured in substeps (1) and (3).