Recognition Equipment Incorp.

Robert B McJohnson

In biphase operations where logic 1's are represented by a logic 0-1 code in a data stream which controls bar code printing, and logic 0's are represented by a logic 1-0 code, the invention involves altering to a logic 0-0 code in the stream each logic 1-0 code which follows a logic 0-1 code. In a more specific aspect, binary information signals are encoded for detection by a reading system effective within a bandwidth of bar densities. Such encoding is effected by sensing each bit time period of the binary information signal, and representing a logic one level occurring within a bit time period by inserting a logic one level in a trailing half of a corresponding bit time period of an encoded signal. If a logic zero level is sensed in a bit time period of the binary information signal after the detection of a logic one level in an immediately preceding bit time period, logic 0's are inserted in the leading and trailing halves of a corresponding bit time period of the encoded signal. Further, if a logic zero level is sensed in a bit time period of the binary information signal after a logic zero level is detected in the immediately preceding bit time period, a logic one is inserted in the leading half of a corresponding bit time period of the encoded signal. The foregoing steps are repeated for each bit time period of the binary information signal.

Modified biphase modulation bar code printer

Bar-code data is read in the presence of noise. An analog output signal from a bar-code sensor has amplitude variations dependent upon the presence and absence of bars as well as upon differences in backgrounds upon which the bars are printed. The output signal is normalized to minimize variations therein, and the normalized signal in turn is converted to a digital signal at a sample interval small compared to the period of the known waveform. An expected response to each bar is of a known waveform. A digital reference set is stored which represents products formed by multiplying each quantization level of the digital signal by each sample of the known waveform taken at the sample interval. For each sample interval along the output signal, members of the reference set are selected dependent upon the sample interval of the known waveform and the corresponding amplitude of the digital signal, and summed to form one point of a correlation output function. The correlation output function in turn is continuously sensed for the presence of predetermined bar dependent characteristics.

Logarithmically normalized cross-correlation bar-code reader

Video signals generated by reading bar coded documents are transformed into pulses uniformly truncated in amplitude and having transitions only at points corresponding to change in sign of the slope of the adjusted video signals. The pulses are utilized to control the state of an output device depending upon whether the integral of any of the truncated pulses exceeds a reference level.

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Dallas, TX, United States of America

Robert B McJohnson