Patent GB-1008489-A (GB)
Title: Scanning apparatus for the automatic recognition of symbols
IPC: G06V30/10
Filed: 1964-04-23
Abstract: 1,008,489. Automatic character reading. SIEMENS & HALSKE A.G. April 23, 1964 [April 26, 1963], No. 16787/64. Heading G4R. In automatic reading apparatus for text consisting of evenly spaced rows of symbols, Fig. 1, on a document P moved upwards relative to the scanner, the scan pattern consists of a series of vertical strokes spaced horizontally to form a sweep across the document each sweep being designed to contain one row and the sweeps are synchronized with the rows by using an initial fast scanning rate giving overlapping sweeps SB1-SB3, signals detected in each scan being stored and recirculated in subsequent scans, to obtain an indication of whether a row lies within a scanning sweep and if it does to reduce the sweep rate so that successive sweeps LB1-LB3 correspond with successive rows. The document moves in the direction of the arrow and a flying-spot scanner makes a succession of vertical scans forming a sweep across the document. Movement of the docu - ment is compensated for by applying an increasing bias to the vertical deflection voltage proportional to the horizontal deflection. The scanning rate is initially such that an area of the document equivalent to a row of numerals is overlapped by two successive sweeps, e.g. SB1 and SB2. When a sweep is made in which a row of characters is detected, the sweeps become slower as shown at LB1, LB2, LB3 so as to register with succeeding lines. The signals derived from the characters are entered into a re-circulating register Rp, having a capacity equal to one vertical scan. As the sweep proceeds, the black signals remain in the store being passed back via a feed-back loop so that the projection of the characters is stored. The feed-back loop is blocked at the end of a character by means as described in Specification 979,178 in which the end of a character is formed by comparing each scan with the stored black signals of previous scans. This is performed by gate Gp10 responding to a black signal in register Rp and a white signal in the present scan. Gate Gp00 responds to white signals in the register and in the present scan and applies a signal to a 1-bit store Sp00. The store provides one input to gate Gp0010; the other is from gate Gp1O The output of gate Gp0010 is applied to counter Zp10 receiving also clock pulses T. The length of black line in register Rp (representing a projection of the character is thereby measured by counting pulses, provided this black line follows an allwhite condition as it would if the character is properly embraced on the upper side by a scanning sweep. If a prescribed minimum count is reached a storage stage Sp10 is set. If the " 1, 0 " condition is followed by a further " 0, 0 " condition gate Gz passes a signal via OR gate OGzSp to AND gate GZP which also receives an input from stage Sp10. The output of gate GZP, stored in stage SZP indicates that a character has been scanned which is wholly included in the scanning sweep. If the black line in register Rp is too long the counter Zp10 does not give an output on the appropriate stage and store SP 10 is not set so that these longer lines are ignored. The conditions necessary to set stage SZP occur in scan n, Fig. 2, at point u, after the next two numerals similarly, and finally in scan 1 at point uu. The stage SZP is set at u and remains set. It indicates that the first row of numerals is located in the scanning sweep and the sweep speed is reduced as described above at the end of the current sweep. If the successive lines of numerals are evenly spaced the successive sweeps automatically remain in register with them. If not the circuit is arranged so that a re-synchronization takes place automatically initiated by the occurrence of a blank sweep which causes a return to the fast sweep speed. Specifications 845,106 and 871,163 are referred to.