Patent ID: 7291831

Claim:
An optical encoding system, comprising: a light source configured to emit light; a code strip, comprising: a calibration area configured to generate a calibration signal, the calibration area having a degree of transparency associated therewith that decreases as contaminants collect on the code strip; an indexing area configured to generate an indexing signal; and an encoding area for generating an encoding signal; a photo detector, comprising: a calibration photodiode configured to convert light transmitted through the calibration area from the light source into an electrical calibration signal, the calibration signal being used to determine the degree of transparency of the calibration area; an indexing photodiode configured to convert light transmitted through the indexing area from the light source into an electrical indexing signal; and an encoding photodiode configured to convert light transmitted through the encoding area from the light source into an electrical encoding signal; a calibration circuit operably coupled to the photo detector and the light source, the circuit being configured to compare the degree of transparency to a threshold value and in the event the threshold value is greater than or equal to the degree of transparency, the calibration circuit further being configured to increase a current provided to the light source increase the brightness of light emitted therefrom in a direction of the indexing area and the encoding area.