| 摘要 |
1507219 Facsimile scanning ASSOCIATED PRESS 17 Dec 1975 [13 Jan 1975] 51629/75 Heading H4F In a receiver of a facsimile system, a laser beam is modulated by an acousto-optical modulator causing the beam to oscillate transverse to its scan direction so as to expose the entire width of the scan line and reproduce a continuous picture free of a line pattern. As described a frequency modulated, radio frequency carrier is amplitude modulated by the signal received from a transmitter and applied to acousto-optical modulator 44, the amplitude modulation causing direct modulation of the intensity of the laser beam and the frequency modulation causing the beam to be oscillated through a small angle (viz spot wobble on a C.R.T.). Mirror 42 scans the beam across the width of photosensitive paper 40 which is moved perpendicular to the scan direction by a roller 48 which is synchronized through logic circuit 54 with the drive to mirror 42. Also described is a transmitter having substantially the same components as the receiver with the exception (i) that photodetectors pick up light reflected from a document and generate an electric signal representative of the intensity variations across the document and (ii) the signal applied to the acousto-optical modulator is frequency but not amplitude modulated. Both the transmitter and receiver can be used in conjunction with known receivers and transmitters respectively. Preferred values are given for spot size, line width and carrier and modulation frequencies. It is stated that the "dither frequency" should be at least 10 times the bandwidth of the signal produced by the line scan alone. |
