Parkhurst & Oliff
Method for reading information or defect out of rotating disc
 In order to read out information recorded on a disc rotating at a constant angular velocity by means of a pick-up head movably arranged in a disc radius direction, a head position on the disc is detected to obtain a position signal representing a distance from a disc center to the pick-up head, and then a pulse signal having a frequency corresponding to the position signal thus obtained is generated. A detection signal supplied from the pick-up head and the pulse signal are supplied to an AND gate and pulses of the gated out pulse signal are counted by a counter. The number of the counted pulses represents correctly a length of the information recorded on the disc irrespective of position of the information on the disc. 
Olympus Optical Co., Ltd.
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G11B G11B G01N G11B G11B G11B
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Ken Shozi Masaharu Kunio Hiroshi Kiichi
Ohsima Yoshikawa Sakamoto Yamamiya Kodama Kato