Patent GB-1418105-A (GB)
Title: Sensing apparatus
IPC: G06K7/10
Filed: 1973-03-29
Abstract: 1418105 Optical bar code reader ELECTRONICS CORP OF AMERICA 29 March 1973 [31 March 1972 17 April 1972] 15221/73 Heading G4M A label carrying bar code markings is mounted on an article carried by a conveyer past reading heads. The label has digit spaces with a bar in the leading half of each space defining a "1" and in the trailing half defining a "0". The data on the label commences with two locating marks A, B with the leading mark A located a predetermined distance from the leading edge of the article. The label is sensed by three reading heads (Fig. 1, not shown) spaced in the direction of travel of the article. The first head reads the markings, the second head detects the leading edge of the article and is situated so that at this point the first head is aligned with the start of the bars and the third head is situated such that when it detects the leading edge of the article the first head is at the end of the bars. The three heads feed circuitry (Fig. 4, not shown) producing a pulse at the commencement of the label, a pulse for each black bar marking on the label and two pulses 154, 156 at the end of the label the latter from two one shots and a delay. The pulses 150-156 on line 148 feed circuitry (Fig. 6) incorporating three ramp generators 180, 182, 184. The first pulse 150 operates ramp generator 184 via flip-flop 196 and via delay 197 enables AND gate 192 to pass the second pulse 152a. This operates ramp generator 180 until the third pulse 152b is received when ramp generator 180 holds its value at a voltage which indicates the speed of the label past the reading heads. This voltage is divided by resistors 202, 204, 206 to feed comparators 214, 216, 218. The third pulse B via flip-flops 186 and 194 operates ramp generator 182 which supplies a second input to the comparators. One shots 224, 222 are then pulsed when the ramp 182 reaches 25% and 75% of the  voltage on line 208. One shot 220 resets ramp generator 182 for each equality from comparator 214 and the ramp generator can also be reset by one shot 190. One shots 222, 224 via OR gate 232 alternately set and reset flip-flop 240 to produce pulses triggering one shots 242, 244 to produce strobe pulses in the first half or the second half of each digit space. One shot 242 samples the data on line 148 in the first half of the digit space and feeds "1"s or "0"s into a shift register 260 shifted by a delayed pulse from the one-shot 242. A flip-flop 300 detects overflow when the shift register is full, stops the shift, pulses and enables AND gates 302-310. The "1"s from gate 250 alternatively set and reset a party flip-flop 264 and set a bit error control flip-flop 286 feeding a faulty bit counter 280. A reset signal 200 is produced when the ramp from generator 184 achieves the voltage on line 208 from generator 180. If a label is not present on the article only pulses 150, 154, 156 are produced. Error counter overflows to produce an output from AND gate 310. If either or both of signals 152a, 152b are missing, i.e. due to lamp failure or irregular triggering by transient light conditions flipflops 354, 364 produce error signals. In a further embodiment (Figs. 8 and 9, not shown) the first bar starts a timer and after a predetermined interval the pulse train is sampled. The following intervals depend on whether a "1" or "0" is detected.