| 摘要 |
1,200,584. Automatic speed control. AMPEX CORP. Feb.26, 1969 [March 1, 1968], No.10225/69. Heading G3R. In a system for controlling a driven member according to a reference signal indicative of the desired condition of the member a secondary control loop is provided to remove unwanted variations in the reference signal. In a system for controlling the speed of the head drum 3 of a video tape recorder, the reference signal 59 is derived from the sync. pulses in the video signal during recording and from a control track of the tape during playback. Irregularities in the reference signal are removed by the secondary control 17 and the resulting reference signal is compared with the output of a tachometer generator 21 in a bi-stable circuit 19, the output of the comparator 19 after intergration controlling the energization of a printed circuit motor 9 driving the drum 3 so that the drum is synchronized with the reference signal. The control 17 includes a variable frequency oscilator 37 supplying the reference signal to the comparator 19. The frequency of the oscilator is set by a voltage normally derived from a pre-set 43 but modified by the output of a comparator 29 whenever the oscilator output differs in phase or frequency from the incoming reference signal 59 so that the reference signal applied to comparator 19 follows the incoming reference in frequency and phase. Since however the feedback loop 17 is relatively slowacting irregularities are removed. If the incoming reference signal disappears, e.g. when the rotating head 5 leaves the tape 7, a clamp circuit 33 suppresses the output of comparator 29 so that oscilator 37 stays at the pre-set frequency. The circuitry of the control 17 is described Fig.3 (not shown) employing transistors.
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