A HIGH-RESOLUTION LATERAL DISPLACEMENT SENSING METHOD USING ACTIVE ILLUMINATION OF A COOPERATIVE TARGET AND A FOCUSED 4-QUADRANT POSITION-SENSITIVE DETECTOR

A method for high-resolution lateral displacement sensing is proposed. The sensor includes an optical transceiver and a piece of reflective sheeting fixed to the object to be measured. The reflector position is measured by illuminating the reflector and focusing the reflected lig ht on a four-quadrant (4Q) position-sensitive detector (PSD). The meth od provides true lateral displacement in a large working volume withou t calibration due to the property of a focused 4Q detector in which th e size of the measurement span is determined solely by the size of the reflector, thus providing inherently accurate, constant scaling indep endent of distance. Experimental results obtained with a laboratory pr ototype show an air turbulence-limited resolution of a few micrometers (s value) and integral and differential nonlinearities better than +/ - 1% and +/- 7%, respectively, when a square reflector of 1 cm2 is use d at a distance of 2.5 m. The main systematic source of error seems to be the spatial nonuniformity of the reflector specific radiance.