Method of determining the elapsed and/or still available playing

Details Method of determining the elapsed and/or still available playing Method of determining the elapsed and/or still available playing

1986-09-22

1988-02-23

Tupper, Robert S.

Dynamic magnetic information storage or retrieval

Miscellaneous

G11B 1500

Patent

active

047274468

DESCRIPTION:

BRIEF SUMMARY
The point of departure for the invention is a method of determining the elapsed and/or still available playing time of a magnetic tape being wound onto a take-up reel from a supply reel by determining the thickness of the tape and the diameter of the spindle. Determining the residual length of a tape still available on the supply reel of a magnetic-tape player is known from U.S. Pat. No. 4,280,159. That method, however, can only be carried out when the recording base is advancing at a constant speed, and the thickness of the base is ignored. The result is errors of unsatisfactory precision in the display.
Displaying the still available playing time in VHS equipment is known. In this case as well, the operation depends on a constant recording-base advance speed. The display switches off during fast rewinding because it is too inaccurate to be useful.
Determining the instantaneous position of the tape from its relation to the coil diameter in Video 2000 models is also known. In this case, however, the total tape supply of a recording base accommodated in a cassette must be known first, meaning that the cassette must be accordingly coded or the supply must be entered manually, which is often impossible because the overall length of the recording base is not indicated on the housing of the cassette. Manual input is also inconvenient and involves additional operations on the part of the user of the recorder.
German OS No. 2 746 613 discloses a method of determining the supply of a magnetic tape. A signal indicating the speed of rotation is derived both from the supply side and from the take-up side during rewinding the two frequency measurements obtained at prescribed intervals are processed. The interval of time between the measurements is long when the tape is running at low speed and short when the tape is running more rapidly. Although the supply is determined by means of digital arithmetic at low tape speed, it is obtained by analog operations at high speed. Even at high tape speed, however, it is important to display the supply with minute precision in real time, and analog arithmetic is too imprecise to be appropriate.
The object of the invention is to eliminate these drawbacks and provide a method that, independent of the speed of advance--during both normal recording and playback and during rapid search and rewinding that is--will make it possible to display elapsed playing time, remaining playing time, and, when necessary, the sum of both informational components with minute precision. This object is attained in the invention characterized in the main patent claim. The advantage is that it provides satisfactorily reproducible displays of the playing times by supplying an instantaneous coil value after only one time measurement during normal operation, from which value only one pulse per revolution is picked up, independent of the winding speed, and added to or subtracted from the only once measured and calculated value. The precision of counting is independent of the speed that the coil is rotating at.
The invention will now be specified with reference to the drawings, wherein
FIG. 1 is a block diagram illustrating the method,
FIG. 2 is a detail of FIG. 1, and
FIG. 3 is a graph of the pulses intended to illustrate the method.
The thickness of the recording base must be determined first. This can be done by means of the method disclosed in Patent Application P No. 3 411 535.8. Once the spindle diameter Do of the particular type of cassette has been established, the time t it takes the spindle to rotate one revolution can be measured. This time varies from coil n to coil n+1 because the rotation time of a coil with a longer diameter will be longer with the recording base advancing at a constant speed.
How spindle diameter Do can be determined will now be specified. Once the tape thickness d has been determined, the times that each tape coil takes to rotate through a complete revolution are measured and added. The resulting time is compared with a table. The fact that there are tapes with thicknesses d=1

REFERENCES:
patent: 4423455 (1983-12-01), Fukuoka
patent: 4479159 (1984-10-01), Kamei et al.
patent: 4532560 (1985-07-01), Williams
patent: 4644436 (1987-02-01), Unno

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