| 摘要 |
PURPOSE:To detect the quantity of a tape without controlling strictly the speed of a rotary head by detecting the quantity of quick traverse and rewinding from the average value of period of appearance of reproduction signals from each track caused by the rotary head, and the number of revolutions of the rotary head. CONSTITUTION:In case of quick traverse in a helical scanning VTR etc., a switch 31 is turned on, and a reproduction signal of each track generated by two rotary heads along loci 51, 52... from a switch 22 is detected by a detector circuit 32. This detected output is processed by a BPF33 and a waveform shaping circuit 34, and average values TOA.n0.TOB.n0 of the period of appearance of reproduction signals from each track generated by each head are determined by a microcomputer 35. The number of revolution signals no of two rotary heads are also supplied to this computer, and the quantity LD of quick traverse of the tape per rotation of the rotary head 1 is operated and detected by formula LD= nD{Vt/TOA.n0+Vt/TOB.n0}/2nD. The same is applied to the quantity or rewinding. Thus, the quantity of the tape at the time of quick traverse and rewinding can be detected without controlling the speed of rotary head. In the formula, Vt is a normal tape speed. |
