Dynamic magnetic information storage or retrieval – Miscellaneous
Patent
1995-10-10
1999-02-02
Heinz, A. J.
Dynamic magnetic information storage or retrieval
Miscellaneous
360 71, 242357, G11B 1518
Patent
active
058673547
ABSTRACT:
A method of and a device for determining the total playing time of a magnetic tape accommodated in a cassette (1) in a magnetic-tape recording and/or reproducing apparatus, for example, a video recorder of the helical-scan type. The tape (4) is moved between a tape spool coupled to a first reel disc (2) and a tape spool coupled to a second reel disc (3), two measurements being carried out. In the first measurement, the tape is moved with a known tape speed. The revolution times (T.sub.l, T.sub.r) of the first and the second reel disc are measured in this first measurement and a parameter is derived which corresponds to the sum of the squares of the revolution times. A cassette-specific constant (.beta.) is derived from this parameter and the known tape speed. In a second measurement, the revolution times of the first and the second reel disc are measured during N revolutions of one of the two reel discs for each revolution of this reel disc. For each revolution, a ratio K(n) is calculated from the revolution times thus determined and the cassette-specific constant, K(n) being proportional to L(n)/L.sub.t and L.sub.t being the total length of the tape and L(n) being either the length already used or the residual length of the tape, where n is an integer and 1.ltoreq.n.ltoreq.N. In an approximation, the N calculated ratios K(n) are approximated by an at least quadratic function in dependence on n and the total playing time is determined from a constant A in the function (K(n)=X+A.multidot.n+B.multidot.n.sup.2 + . . . ) thus obtained.
REFERENCES:
patent: 4996611 (1991-02-01), Ito
patent: 5165622 (1992-11-01), Arai
Belk Michael E.
Heinz A. J.
U.S.Philips Corporation
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