Optical encoder with digital gain compensation controlling source

Abstract

In an optical encoder with a single light source, an array of a plurality of spaced photodetectors formed on a common substrate, a reticle disposed in fixed position relative to said photodetector array, and a scale of alternating translucent and opaque regions relatively moveable between said light source and said reticle so as to cause said array to provide a plurality of phase related analog signals whose amplitudes vary with the position of said scale, an improved digital automatic gain control is disclosed. A digital switch selects one of said analog signals and an analog to digital converter converts and puts out the selected signal as a digital value. A programmed microprocessor reads each such digitized signal, determines the signal value corresponding to maximum light transmission, compares said value with a nominal reference value, and computes a correction value therefrom. The microprocessor stores said correction value and thereafter puts it out as a digital value to a digital to analog converter which converts it into an analog electrical signal. An amplifier drives said light source in accordance with each said analog electrical signal, so that the optical encoder operates said single light source to yield a light value which has been digitally measured and corrected to a nominal value for each photodetector of said array.