Methods for the Reduction of Paper Noise in a Bar Code Scanner
Original Publication Date: 1989-Feb-01
Included in the Prior Art Database: 2005-Jan-27
A holographic bar code scanner can provide a large effective depth of field by having individual facets on the holographic disk focus at different distances from the disk. To achieve satisfactory performance throughout the full depth of field of the scanner, the laser beam diameter at the holographic disk must be large enough to yield acceptably small focussed beam diameters at the longest focal lengths. In a large-depth-of-field scanner, this will result in extremely small beam diameters at the shortest focal lengths. This creates a problem when scanning bar codes on rough textured surfaces, such as normal paper, as the small scanning spot will "see" the surface texture. This adds "paper noise" to the light reflected from the bar code, lowering the probability of getting a correct scan and decode.