Method and apparatus for reducing the number of rejected documents when reading bar codes

摘要

This specification describes apparatus for reading and decoding data encoded in terms of the spacing between adjacent code bars on a document. The apparatus contains reading means for producing an electrical pulse for each bar recorded on the document as the bar passes the reading element. A counter is used to measure the time between each two pulses and the resultant counts are stored in a memory in the order in which the pulses were produced by the reading means. A microprocessor then compares this stored data with microcoded data representative of properly coded digits. If there is a compare the stored data is shifted out of the memory and into a computer for use. However if there is a no-compare the microprocessor alters the data on the assumption that a particular type of error has occurred and again compares the modified data with the microcoded data. If this results in a compare the modified data is again read out and into the using computer. However if it again results in a no-compare, the processor modifies the stored data a second time on the basis of another assumption and this newly modified data is compared with microcoded data. These successive data modifications and their comparisons to the microcoded data continue until a compare occurs or it is apparent that the encoded data is not retrievable by the decoding apparatus.