Patent GB-1181887-A (GB)
Title: Facsimile Transmission System
IPC: H04N1/40
Filed: 1967-11-28
Abstract: 1,181,887. Facsimile systems. INTERNATIONAL BUSINESS MACHINES CORP. 28 Nov., 1967 [12 Dec., 1966], No. 54006/67. Heading H4F. A facsimile system comprises a scanner 10 for repetitively scanning each line of a document 48 until incremented to the next line, an encoder 12 for encoding signals from the scanner, a buffer 14 for storing the generated codes, a register 20 for transferring codes from the encoder to the buffer and from the buffer to means 22 for transmitting the codes, and a control unit 26 including means responsive to an indication that the buffer is able to accommodate a complete new line of codes to initiate encoding at the beginning of a line scan and means for incrementing the scanner to the next line at the completion of encoding of the complete line scan. The state of the buffer is indicated by a counter which is advanced in count in response to a control signal RC from encoder 12 each time a code is produced for entry into the buffer and which is reduced in count in response to control signals CT from the transmitting means 22 each time a code is read out from the buffer. The counter prevents operation of the encoder until the buffer state is low. When the encoder is placed in operation the codes for one of the scan line are entered in the buffer and then the scanner is advanced to the next line. Signals produced as a result of repetitive scanning of lines are ignored until the one line scan when the encoder is set into operation. The counter also prevents the read-out of codes until the buffer contains sufficient for operation of the transmitting means. The signals from the scanner are translated to binary form by converter 11 and then encoded in 12 according to run lengths to produce parallel seven-bit numbers on leads 16. An eighth bit is provided to indicate whether a run length is black or white. The scanner produces clock pulses CB and these are gated to the encoder as pulses CE when the encoder is to be placed in operation. Each operation of the control unit 26 by signal RC or CT causes the production of a buffer address signal A, a sequence of clock pulses C1-C8 to time the readin or read-out of the code bits, and signals ED and BD to actuate the register. The codes are read into the buffer over leads 18 and read-out over leads 19. During read-out the register functions to translate the code bits from parallel to serial form suitable for transmission. The transmitting means supplies eight signals CT to read out one code, provision being made, however, to reduce the buffer content counter by only one for the eight signals. The entry of codes into the buffers may interleave with bit transfers to the transmitting means. The scanner and encoder are capable of generating codes at a rate in excess of the rate at which the transmitting means can transmit the codes. The scanner illuminates the document by a source 30 and effects scanning by a lens 52 traversed in the line direction by continuously driven belt 40. The document signal is produced by photo-cell 50. The belt contains a series of slots 54 which generate the clock signals CB in a second photo-cell 60, and a further single slot 56 which generates left- and right-hand margin signals ML and MR in third and fourth photocells 58 and 64. These later two signals function via the control unit to ensure that encoder 12 is placed in operation for one line only, and that at the end of the line a signal I is produced which actuates a motor 72 to stop the scanning mechanism through the distance of one line. Control unit 26 is described more fully with reference to Fig. 3 (not shown).