Bar code reader with compensation for signal variation on different scan lines
AssigneeSpectra-Physics, Inc.
InventorsCraig D. Cherry, P. Guy Howard
Life of this patent
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Abstract
A method and apparatus for obtaining a more uniform output signal strength among various scan lines of a multiple scan line laser bar code reader involves switching of the gain level in the return signal amplifier of the bar code reader apparatus, in accordance with the position of the laser beam in the scanning sequence and in accordance with known information relating to the relative response that can be expected from each different scan line. This enables a better uniformity in signals from the reading of bar codes, regardless of which scan line was used to read the code, by compensating for inevitable variations in return signal strength on different scan lines, particularly in a shallow-profile slot scanner.
Claims10
In a laser bar code scanner having a laser generating a beam, scanning means for moving the beam along more than one scan line, and a received signal amplifier for processing the signal received from the beam after reflecting off a bar code being read, an improved signal detection system, comprising:
- beam position detector means for detecting the position of the laser beam in a scanning sequence, and
- gain switching means for adjusting the gain of the received signal amplifier in accordance with the beam's position in the scanning sequence and with predetermined information regarding different signal strengths that can be expected at different beam positions in the scanning sequence,
- whereby a more uniform signal can be achieved in bar code reading on multiple scan lines.
A method of compensating for variations in return signal strength in a laser bar code reader which scans a laser beam along more than one scan line, comprising,
- sensing a cycle "start" position in the scanning sequence,
- from the "start" position determining when the laser beam is on each respective scan line in the sequence,
- predicting variations in return signal strength for each respective scan line, based on predetermined information correlated to each scan line, and
- adjusting the gain of a return signal amplifier of the bar code reader for each scan line, in accordance with and in compensation for such predicted variations in return signal strength.
A method of compensating for variations in return signal strength in a laser bar code reader which scans a laser beam along more than one scan line, comprising,
- determining the position of the beam in the scanning sequence,
- predicting variations in return signal strength for each respective scan line, based on predetermined information correlated to each scan line, and
- adjusting the gain of a return signal amplifier of the bar code reader, based on position of the beam in the scanning sequence, for each scan line, in accordance with and in compensation for such predicted variations in return signal strength.
Dependencies are inferred from the claim text.