Browse Prior Art Database

Time Multiplexed Two Beam Scanner

IP.com Disclosure Number: IPCOM000048641D
Original Publication Date: 1982-Feb-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Broockman, EC: AUTHOR

Abstract

This article describes a holographic scanner in which the beams produce by two dissimilar lasers are time multiplexed before reaching the halographic disc. The spatial position of a scan pattern produced by a rotating holographic disc is a function of the holographic recordings and of the frequency of the laser beam which impinges on the disc. Where time multiplexed red and blue laser beans are used with a single rotating holographic disc, the patterns produced by the two lasers will be slightly shifted relative to one another to provide one extremely dense "superpattern".

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Time Multiplexed Two Beam Scanner

This article describes a holographic scanner in which the beams produce by two dissimilar lasers are time multiplexed before reaching the halographic disc. The spatial position of a scan pattern produced by a rotating holographic disc is a function of the holographic recordings and of the frequency of the laser beam which impinges on the disc. Where time multiplexed red and blue laser beans are used with a single rotating holographic disc, the patterns produced by the two lasers will be slightly shifted relative to one another to provide one extremely dense "superpattern".

Referring to Fig. 1, coherent light beams produced by laser A and laser B are applied to a chopper or multiplexer 10 which permits only one of the beams at a time to pass to a binocular-type beam-converging device 12. The output beam from the binocular-type device 12 is applied to a beam from a small mirror 16 toward a rotating holographic disc 18. The disc 18 deflects the incoming beam along arcuate scan lines. In practice, the deflected beams are folded by an array of stationary mirrors to produce a complex scan pattern suitable for reading bar- coded labels printed on grocery items, such as carton 20. For ease of illustration, the array of stationary mirrors is omitted from the drawing.

Light retro-reflected from the carton 20 is transmitted back through the holographic disc 18. Most of the returning light bypasses the small mirror 16 and impinges on a light detector 22 which produces an electrical signal which can be processed in a signal processing unit 24. Depending upon the speed with which chopper 10 time multiplexes the outputs of lasers A and B, it may be necessary for signal processing unit 24 to know which beam is being returned from the item being scanned at any given time. A sensor 26, connected to chopper 10, provides this information to the signal processing unit 24 in a manner which will be described in more detail below. The output of the signal processing unit 24 is typically a label candidate signal which is applied to a point of sale (POS) system 28 which uses the label candidate signal for price look-up, inventory control, etc., functions.

Depending upo...