| 摘要 |
1146843 Recording and playback MINNESOTA MINING & MFG CO 28 March 1966 13606/66 Addition to 1146842 Headings G3R R31F R62 R69 and R4 A disc record 10 bearing a spiral recorded track produced generally as described in Specifications 1146842 and 1146841 is rotated so as to be scanned by a beam of energy (e.g. light) which is directed from a source 208 to a pick-up 212-220 by way of the record, a radial drive 206, 207 causing the beam to follow the spiral track, and the pick-up comprising two sensors (e.g. photoelectric cells) 218 and 220 which receive equal amounts of energy when the beam is accurately centred on the track and means Fig. 4, (not shown) for comparing the outputs of the two sensors to derive an error signal by means of which the radial drive is controlled so as to tend to maintain the beam accurately centred on the track. The error signal is used also to control vertical, as shown in Fig. 5, adjustment of a wedge-shaped mirror 216 which divides the beam between the two sensors 218 and 220, the adjustment tending to equalize the amounts of energy delivered to the two sensors. A second error signal representative of deviations of the sensor outputs from synchronization with a reference signal is used to control horizontal adjustment of the mirror 216 so as to tend to eliminate such deviations. This second error signal is produced by comparing the output of an oscillator with the response of the sensors 218 and 220 to synchronizing pulses recorded on the record 10. |
