Apparatus and method for automatic gain control during scanning

Abstract

The disclosure describes an apparatus and method for automatic gain control during scanning. The apparatus comprises an optical detector to receive an optical signal reflected from a symbol positioned within a scan window by an optical beam scanned from a leading edge of the scan window to a trailing edge of the scan window; and a processor coupled to the optical detector to adjust the gain of the optical detector during the beam scan. The process comprises receiving an optical signal using an optical detector, wherein the optical signal comprises optical energy reflected from a symbol positioned in a scan window as an optical beam scans from a leading edge of the scan window to a trailing edge of the scan window, and adjusting the gain of the optical detector during receipt of the optical signal. A calibration process is disclosed comprising calibrating the optical detector to obtain a plurality of gain corrections, each gain correction corresponding to a different position between a leading edge and a trailing edge of a scan window, and storing the plurality of gain

Description

TECHNICAL FIELD The present invention relates generally to scanners, and in particular, but not exclusively, to automatic gain adjustment during scanning. BACKGROUND Bar code scanners typically function by generating a thin beam of light and scanning the beam across a symbol to be read. The symbol typically comprises a plurality of alternating light (usually white) and dark (usually black) areas; the best-known symbols are bar codes, where the light and dark areas are formed by a white background with alternating black bars superimposed thereon. As the spot created by the projection of the beam onto the symbol travels across the symbol, it crosses the alternating light and dark areas and a portion of the light hitting the symbol is reflected back into the scanner. More light is reflected from the light areas than from the dark areas, so the optical energy reflected back into the scanner will consist of a signal containing a series of peaks corresponding to the light areas and vall...

AI Technical Summary

Benefits of technology

The disclosure describes an apparatus and method for automatic gain control during scanning. The apparatus comprises an optical detector to receive an optical signal reflected from a symbol positioned within a scan window by an optical beam scanned from a leading edge of the scan window to a trailing edge of the scan window; and a processor coupled to the optical detector to adjust the gain of the optical detector during the beam scan. The process comprises receiving an optical signal using an optical detector, wherein the optical signal comp

Problems solved by technology

As a result, the amount of optical power received at the scanner drops off significantly at the edges of the symbol, making it difficult to adequately scan, capture and decode the information contained near the edges of the symbol.

The problem is particularly acute when the scanner must operate in very close quarters and must therefore be placed very close to the symbol.

Thus, in scanners having a short focal length and operating near the symbol it is particularly challenging to properly read the edges of the symbol. FIG. 1B illustrates the effect of the above phenomenon on the optical response of the scanner.

In other words, there is no way of adjusting the gain during a scan.

This approach therefore cannot be used to address the problem of compensating for reduced optical response at the edges of a scanned symbol.

In addition, even if a standard AGC could be adapted to compensate for gain changes during a scan, they would be much too slow.

First, increasing the power of the laser near the edges of the symbol has serious safety implications because the increased laser power can pose a danger to the eyes of the scanner operator or other bystanders, and when the beam nears the edge of the symbol more of the optical power is likely to be reflected into someone's eyes.

Second, using the laser at a higher power output and continually cycling the laser between low and high power states will decrease the lifetime of the laser and the scanner, ultimately driving up costs to the end user.

Finally, the higher power output of the laser means additional power consumption and additional heat dissipation problems.

Power consumption and heat dissipation both can lead to additional expense in making and using the scanner, as well as inconvenience to the user who, in the case of a hand-held scanner, must carry the additional weigh of heat sinks, etc, used to dissipate the heat created by the additional power consumption of the laser.

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