Browse Prior Art Database

Dual Source, Single Detector Item Sensor

IP.com Disclosure Number: IPCOM000049407D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 37K

Publishing Venue

IBM

Related People

Brookman, EC: AUTHOR

Abstract

This article describes a dual-source, single detector item sensor for a supermarket scanner. The detector can distinguish between forward and backward item flow.

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Dual Source, Single Detector Item Sensor

This article describes a dual-source, single detector item sensor for a supermarket scanner. The detector can distinguish between forward and backward item flow.

The figure is a partial top view of a checkout scanner. Grocery items normally moving in the direction of the arrow 10 are scanned by a laser beam at a scanner window 12. An item detector output can start a scanning operation. The item detector includes a first light source 14 which produces a light beam S1, which is reflected from mirrors 18 and 20 before being returned to a photodetector 22. The light source 14 is driven by a power source having an output frequency on the order of 210 Hertz.

The item detector includes a second light source 24. The output beam S2 from light source 24 follows the beam path between mirror 20 and the detector
22.

The light beam S1 is "modulated" at the frequency of its driving driven at a much higher frequency than 210 Hertz, and S2 is "modulated" at this higher frequency.

The output from the detector 22 is applied to bandpass filters 8 and 30, which separate the S1 and S2 components. The outputs of the filters 28 and 30 are applied to inputs of comparator amplifiers 32 and 34, respectively. A high level signal is produced at the output of comparator amplifier 32 when the light impinging on detector 22 includes the S1 signal. The comparator amplifier 34 produces a high level output signal when the light incident on detector 22 includes the high frequency S2 signal.

By monitoring the S1 and S2 signal levels and the times at which those signals change, the direction of item movement can be determined. Table 1 summarizes even...