Patent GB-1156230-A (GB)
Title: Scanner Control Apparatus
IPC: G06V30/146
Filed: 1968-01-04
Abstract: 1,156,230. Character recognition. INTERNATIONAL BUSINESS MACHINES CORP. 4 Jan., 1968 [9 Jan., 1967], No. 661/68. Heading G4R. Control apparatus for a pattern scanner comprises means for moving the scanner in a forward direction at a relatively high speed when no pattern is intercepted, subsequently in a reverse direction at a relatively low speed after a pattern has been intercepted, and subsequently in the forward direction at the low speed over the intercepted pattern. The invention permits large gaps in a line of characters being scanned for recognition purposes, to be traversed at high speed. In Fig. 1, cathode-ray tube 14 scans the line from right to left using a raster of vertical scan lines. Character separation apparatus 20, as in Specification 1,144,319, which is referred to, is fed by photomultiplier 16 to indicate a blank character space (i.e. a gap large enough to contain a character), the end of a character ("segment") and presence of a character. Counter 22 counts blank character spaces, being reset to zero by a segment signal, and on a count of two sets flip-flop 24. Subsequent presence of a character sets flip-flop 28 via AND 26. The raster scan is set to high speed (i.e. large pitch) by AND 30 when flip-flop 24 is set but 28 is not, i.e. after two consecutive blank character spaces have occurred, until the next character. When flipflop 28 is set, the scanner is reversed via OR 36 and set to low speed (i.e. small pitch). The scanner thus backs-off from the character encountered and when it has completely backedoff, the absence of the character present signal causes, via inverter 32, AND 33 and single-shot 34 the scanner direction to be reversed again so that low speed scan in the forward (right to left) direction ensues for recognition. AND 33 and inverter 32 may be replaced by the delay 35 as shown. A second embodiment combines the above with the vertical centring features of Specification 1,156,229, which is referred to. The right to left scanning of the line (with left to right backoff) is preceded by a left to right scanning which is at high speed until the first character is encountered, then at low speed for a fixed number of scan lines with vertical centring every scan line, then at high speed until the right margin (field bar) is encountered with vertical centring every 7th scan line. The right to left scanning now follows at low speed with vertical centring between characters, for recognition purposes, until a count of two adjacent blank character spaces switches the scan to high speed. When the next character is encountered however, the scanning continues to the left at low speed for X scan lines then reverses and travels at low speed for X scan lines to the right. Once these further X scan lines have been traversed, the system can respond to the absence of a character to reverse direction again and continue the slow leftwards scanning for recognition purposes (with vertical centring between characters). The 2X movement is to permit extra vertical centring (first at every scan line, then every 7th scan line, during the 2 X movement).