| 摘要 |
1,211,277. Automatic position control. INTERNATIONAL BUSINESS MACHINES CORP. May 21, 1968 [June 19, 1967], No.24079/68. Heading G3R. In a system in which deviations of a transducer from alignment with an information record track are detected and automatically corrected, false indications arising when a portion of the record is missing or obscure render the automatic control inoperative. In Fig.1, information stored in digital form as tracks 1-4 having alternate opaque and transparent portion 12, 13 on a film 10, is retrieved by a flying spot 15 influencing a photo-multiplier the mean output of which increases or decreases if the scan deviates toward the edge of a track as shown at 30, 31. In Fig.3, the flying spot from scanner 16 passes through the film record 10 to influence the read photo-multiplier 19. A second reference photomultiplier 20 influenced directly by light from the scanner provides a signal 21 for application to a controller 22 maintaining constant spot intensity, and also provides a signal 25 for comparison with signal 25a from the read photo-multiplier. Any variation of this comparison due to movement of the spot toward the edge of the track is detected by a differential amplifier 32 the output of which is integrated at 36 and serves to restore the scan toward the centre of the track. The control signals are reversed in sense by a controller 34 operating a switch 26 as each successive track is read. Information missing from a portion of a track gives rise to an excessive deviation from the mean signal level which is detected in magnitude and sense by detectors 41, 48, 49 and associated logic circuits, so that a one-shot pulse generator 47 applies a signal 58 to adjust the scan in the appropriate sense to cancel the false correction which will have been produced by differential amplifier 32. The output from generator 47 also causes operation of switch 26 to prevent further automatic control of scan until information is detected again or until the end of the track is detected by counting signal pulses at 44. Application to thermoplastic or magnetic records is referred to. |
