Patent GB-973206-A (GB)
Title: Character recognition apparatus
IPC: G06V30/224
Filed: 1963-10-16
Abstract: 973, 206. Automatic character reading. NATIONAL CASH REGISTER CO. Oct. 16, 1963 [Nov. 19,1962], No. 40866/63. Heading G4R. In a character reader of the kind in which a scanner makes a series of sweeps across a character, deriving signals representing sections through the character there are means for storing the first signal produced by a character and comparing it with the corresponding signal in the next scan and for producing an error signal if, in the successive scans, the signal does not appear at corresponding times. The apparatus is generally similar to that described in Specification 932,414 the characters printed in rows of light across a tape 12 Fig. 3 being projected on to an optical dissection device including a rotating drum 20 having a number of groups of four holes 22, there being light guides to convey light passing through the holes to photocells. The holes 22a, 22b, 22c, 22d sweep across the row of characters as shown in Fig. 8 and recognition takes place when the tape feed has brought the characters to a position where they are cut by the middle two holes and missed by the upper and lower holes 22a, 22d. Two successive scans are shown in Fig. 8 indicated by the numbers 1 and 2. The first signals of each character start a pulse generator which drives a counter. The counter counts up to 15 to give a character cycle. It then resets, stopping the pulse generator, which is immediately started again by the next character. The clock pulses are taken in groups of three to define five sampling zones U, V, W, X, Y and signals produced by the photo-cells corresponding to the middle two holes are gated out at these times to set ten flip-flops. Towards the end of the character cycle the signals from the ten flip-flops are recoded to identify the character and provide an equivalent combination of signals on five leads which are stored in five flip-flops in a buffer store Successive characters are read out of the buffer store into successive columns of a core matrix store having 5 rows and eight columns. A magnetic storage track 400, Fig. 7 formed on the scanning drum is used to delay each scan signal by exactly one scan. The first signal or signals of each character, called the trigger signal G, are applied to a one-shot circuit 402 making a pulse WS, 30 u secs long, which is applied to write head 406 and recorded on the band 400. At the time the next row of holes is making a scan the read head 410 passes the previous scan to one-shot circuit 416 to make a pulse RS, 30 u secs long. Two successive scans are shown in Fig. 8, the trigger pulses for each character for the first scan SC1 are shown at WS<SP>1</SP>. The previous scan trigger signal from read head 410, shown at RS, should coincide exactly with the pulses WS1. In the second scan SC2 a spurious mark 426 is detected by the scanning hole 22b and a false trigger signal is produced to start the counter giving the character 'cycle. For following characters the counter restarts when the left hand side of the previous character is detected. Accordingly false groups of signals are obtained and incorrect characters identified. The pulses WS2 for these scans therefore begin too early. An exclusive OR gate 408 passes the combined pulse 430 to a "hold-over" circuit which responds if its input signal lasts for more that 15 u secs. The output 432 of circuit 420 is used to set "character substitution error" flip-flop ES. This may be connected to control the apparatus in a number of ways. It may cause a full rescan, that is the tape feed motor is reversed and the row is passed through the scanning position again, there being enough free-play in the mechanism to make it likely that a small mark . such as 426 may be missed by the scans in the next reading. The number of times an error is detected is counted and after eight attempts at correct reading the apparatus passes on to the next row. The data corresponding to this row, stored in the core matrix is cancelled. In a second mode of operation entry of the data corresponding to the error character into the core matrix is prevented. If the row was correctly read in a previous scan there is no need to alter the matrix store and means are provided to prevent the error character from being lost. In a third operation rescanning is initiated only if the character giving the error is not already read, it being presumed that a reading made by a previous scan is correct. The apparatus can be adapted for use with a reversed tape, the direction of rotation of the scanning drum being reversed to take re-count of this. This necessitates a second write head 404 Fig. 7 for the band 400 which is used in place of head 406.