Patent GB-1417439-A (GB)
IPC: B07C3/14
Filed: 1973-07-30
Abstract: 1417439 Label reading system FERRANTI-PACKARD Ltd 30 July 1973 [31 July 1972] 36112/73 Heading G4M Labels on packages travelling on a conveyer are read by a television camera which is arranged over the conveyer so that its field of view will include the whole of a label on a package (Fig. 1, not shown). The video output signal O1 for each line scan is fed to a converter 1 which compares voltage levels with a reference and produces a digital "1" for values above the reference and an "0" for values below at output D (Fig. 3c) and the inverse of output D at output I. The label used has longitudinal bars C along each longitudinal side which can carry humanly readable markings in a colour indistinguishable to the machine from the background colour of the bar and has two parallel tracks of markings. A mark is present in both tracks at the start of a label but otherwise a mark in one track has an associated space in the other for error detection purposes (Fig. 2, not shown). The digital signal from output D is fed to gate 4 along with clock pulses from source 46 arranged to produce as shown in Fig. 3 six pulses during scanning of each bar C and twelve pulses between the bars so that a mark A has a nominal pulse width of six. Clock pulses pass through gate 4 when enabled by detection of a dark bar or mark and are counted in counter 7. Decoder 8 supplies an output when a count of 5, 6, 7, or 8 is achieved to account for variation in location bar width due to skew and feeds gate 10 enabled by a clock pulse from AND gate 3 when the light portion following a dark bar is detected. Counter 7 is reset by the same pulse after passing delay 6. If a location bar C is detected counter 11 supplies a signal at its "1" output and clock pulses are fed to counter 14 which for count values of one to sixteen enables AND gate 18 to supply shift pulses via register 5 and for count values 0 and 17 to 24 enables AND gate 10. The count values 17 to 24 correspond to the possible position, taking account of skew, at which the trailing edge of the second location bar C is located. For a count value of 25 counters 14 and 11 are reset. During counts 1-16 pulses from AND gate 2 are shifted into sixteen stage shift register 5 so that the pattern of pulses stored therein corresponds to the absence of marks A, B on the document. Alternatively gate 2 could be fed from the I output of the converter in which case the pattern corresponds to the presence of marks. During counts 17 to 24 if a valid second location bar is detected counter 11 is incremented to 2 and enables AND gate 26. AND gate 26 is also enabled by line counter 22 via decoder 23 when the counter contains values 40 to 200 inclusive in each frame. Counter 19 is then enabled to count frame lines to determine if the label lies in the field of view of the camera. When a minimum number of lines is counted, e.g. 120, a signal is provided indicating that during the next field register 5 contains information from a correctly positioned label. The light source may be flashed to prevent blurring occurring due to movement of the label. Skew detection.-Counter 22 counts the number of lines being scanned and enables gates 21, 24 at count values 102 and 150 respectively. Each gate passes clock pulses on receiving an enabling signal from gate 26 so that the distance from the edge of the second location bar to the edge of the television frame is determined. The gates 21, 24 fed up and down inputs respectively of counter 25 or may feed separate counters and the difference in count value is used to decide whether the skew is in tolerance.