Browse Prior Art Database

Bar Code Scanner Lens Aperture

IP.com Disclosure Number: IPCOM000051407D
Original Publication Date: 1981-Jan-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Routt, WM: AUTHOR

Abstract

The bar code scanner consists of a system for illuminating an area on a coded document upon which a bar code pattern has been placed, and for imaging a portion of the area onto a photosensitive device in such a way that when the scanner is moved properly with respect to the coded pattern, electronic signals corresponding to the code pattern transitions are produced by the photosensor (P.S.). The imaging optical system is usually provided with lenses focusing the light reflected from the pattern into the photosensor. The degree to which light received by the photosensor is restricted to the desired area of the document is determined by lens quality and tolerances, and is strongly affected by displacement of the coded document from the point of best lens focus.

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Bar Code Scanner Lens Aperture

The bar code scanner consists of a system for illuminating an area on a coded document upon which a bar code pattern has been placed, and for imaging a portion of the area onto a photosensitive device in such a way that when the scanner is moved properly with respect to the coded pattern, electronic signals corresponding to the code pattern transitions are produced by the photosensor (P.S.). The imaging optical system is usually provided with lenses focusing the light reflected from the pattern into the photosensor. The degree to which light received by the photosensor is restricted to the desired area of the document is determined by lens quality and tolerances, and is strongly affected by displacement of the coded document from the point of best lens focus.

Both resolution and variation of resolution with document displacement can be improved by the placement of resolution-enhancing apertures in the optical path to block light paths farthest from the optical axis. Of course, this decreases the total light power through the system. However, proper sizing and shaping of the aperture can enhance the optical system resolution while minimizing the attendant loss of power.

For many imaging applications, the object field possesses a nearly circular symmetry, and this dictates that the system apertures be circular. For the bar code system, however, the object field symmetry is decidedly non-circular, i.e., resolution requirements are different between the width and length...