Bar code reader system.

摘要

A reader system for optically scanning a bar code and processing the resulting video signals to produce corresponding digital signals is disclosed. The scanner comprises a camera (18) having an image sensor which converts the varying black and white bar code image into a corresponding analog video signal. This signal is fed to a dynamic threshold detector (40) which tracks the midpoint voltage value of the video signal and applies this value to a comparator (42), where it is compared to the analog video signal. The output of the comparator provides a train of logic states "0" and "1" representing video levels below and above the midpoint voltage value, respectively, thus producing a digitalized video signal corresponding to the bar code. The digital signals are filtered to mask single bit aberrations, with the filter (46) producing a series of logic "0" 's and "1" 's at the clock rate of the system, each of which represents the output of a single "pixel", or picture element, of the image sensor, the output level indicating whether the pixel has sensed a black or white bar.

The number of consecutive pixels having "0" or "1" output levels are counted (54) and compared to preset values to determine whether wide or narrow code bars are being sensed, and this information is stored in digital form in one of two serial memories (70, 72). At the same time, the total number of bars scanned is counted (84). and the memory is inhibited when the count equals the number of bars in the code.

At the completion of a first scan of the bar code image, the storage of information is switched to the other serial memory and the bar code scanning process is repeated while the data just stored in the first memory is processed, for example, in a conventional bar code-to-numeric or alphanumeric converter for display. Multiple scans of the bar code insure an accurate readout.