| 摘要 |
1330328 Automatic control of speed BLAUPUNKT-WERKE GmbH 21 Dec 1970 [19 Dec 1969] 60651/70 Heading G3R The speed of a rotating head 13 in a video tape recorder is controlled in response to the phase difference between signals representative of head position (generated at 14) and reference signals, the "gain" of the system as a whole, i.e. the magnitude of the output (controlling) signal, being substantially constant for high frequency fluctuations. Pulses produced at 14 are shaped by transistor 16 and applied to the base of a transistor 18, to the collector of which is applied a ramp signal from a generator (not shown) synchronized with the frame synchronized signals in the video signal (either original or recorded). According to the height of the ramp where the pulses from 14 occur, a control signal voltage is established on a capacitor 19, and is applied to the base of an amplifying transistor 20. In the prior art this controls directly the conduction of further transistors 21, 22, the latter being in series with a retardation winding 23 which thus controls the speed of head wheel 13. It is explained that this arrangement would not correct a phase drift so the present invention provides a differential amplifier 31, 32, one side of which is biased by a potentiometer 36 so that balance occurs when the pulse from 14 occurs "half way up the ramp". Thus, a phase drift produces correction in the appropriate direction. A negative feedback loop comprising a capacitor 37 and resistor 38 effectively reduces the gain of the system for more rapid speed changes. |
