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Two Sensor Bar Code Scanner Using Sensor Spacing as a Reference

IP.com Disclosure Number: IPCOM000082474D
Original Publication Date: 1974-Dec-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 69K

Publishing Venue

IBM

Related People

Kulikowski, RJ: AUTHOR [+2]

Abstract

In one form of retrospective pulse modulation, bars and spaces of width d and 2d are defined as representing a binary "1" if an adjacent bar and space are of the same width, and a binary "0" if an adjacent bar and space are of different widths. These bars can be scanned by a hand-held scanner having two sensor apertures of negligible width which are spaced 3d apart.

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Two Sensor Bar Code Scanner Using Sensor Spacing as a Reference

In one form of retrospective pulse modulation, bars and spaces of width d and 2d are defined as representing a binary "1" if an adjacent bar and space are of the same width, and a binary "0" if an adjacent bar and space are of different widths. These bars can be scanned by a hand-held scanner having two sensor apertures of negligible width which are spaced 3d apart.

Fig. 1 shows circuitry for implementing a two-sensor method of decoding this form of retrospective pulse modulation. Bar and space edge detectors 11, 13, 15 and 17 detect the leading edge transitions as bars and spaces pass under sensors A and B. The output of bar edge detector 11, labeled AB, is delayed by delay circuit 25 to reset free-running counters 21 and 29, so that they begin counting from zero whenever the leading edge of a bar is detected at sensor A. Likewise, the output AS from space edge detector 13 is delayed by delay circuit 35 to reset free-running counters 31 and 39, so that they start counting at zero whenever the leading edge of a space is detected at sensor A.

When the leading edge of the bar which has been previously detected at sensor A is detected at sensor B, bar edge detector 15 provides an output BB which opens gates 41 and 43 to transfer the then present contents of counters 21 and 29 into registers 45 and 47.

The counts in registers 45 and 47 are proportional to the distance between sensor apertures A and B of the hand scanner. Likewise, when space edge detector 17 provides an output BS to AND gates 49 and 51, the accumulated counts in counters 31 and 39 are transferred to registers 53 and 55, respectively. The contents of registers 53 and 55 are also proportional to the dimensions between sensors A and B in the hand scanner, but the proportionality constant may be different due to acceleration of the hand-held scanner.

When bar edge detector 11 senses the edge of a second bar, the output

opens gate 19 to transfer the total count...