Importance

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Abstract

A light beam, typically 780 nanometer coherent light generated by a laser diode, is focused, preferably by a wide angle graded index optics lens having a numerical aperture of 0.46 and a diameter of 1.8 mm, into a diffraction limited spot, of approximate diameter 0.039 to 0.3 mils, upon an encoder wheel. The encoder wheel is typically a photoetched radial reticular grating on Mylar.RTM. plastic having lines at 0.00025' width at a radius of 1'. The focused light beam intercepts the encoder wheel at this 1' radius and is alternately transmitted and obstructed by the reticular grating of the rotating encoder wheel. The selectivity transmitted light beam is received at a detector, typically a phototransistor. Greater than 10,000 transitions per encoder wheel revolution are detectable.

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First Claim