| 摘要 |
<p>1452330 Automatic control PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 8 Nov 1973 [11 Nov 1972] 51850/73 Heading G3R In a system for reading a disc shaped record carrier 1 the tangential position of an information scanning point a is controlled in response to a periodic signal derived from a track on the disc, the signal being filtered such that the control system as a whole has a band pass characteristic, the frequency corresponding to the speed of the disc lying within the pass band. The object is to cause the scanning point to follow eccentricities or speed variations of the disc without the use of a reference oscillator, which is prior art. The embodiment also provides for radial positioning and the disc may be magnetic although an optical system for a video signal is described. Light from a source 4 is reflected at 5, 6, 9 and 11, several tracks of the record 1 at point a being imaged on photo-electric detector 18. The signal from 19 is used for tangential control and 20 for radial control. Horizontal synchronized pulses from the video signal are separated at 26 and filtered as specified at 27 to control the energization of windings attached to mirror 11, which is in a magnetic field Fig. 3 (not shown). The radial control is not fully described, but the outputs from photo-cells 20 control the angle of mirror 9. It is mentioned that radial control can be effected from the tangential system, using a 90 degrees lag.</p> |
