Next Generation, High Accuracy Optical Tracker for Target Acquisition and Cueing

摘要

A critical need exists for a fast, cost-effective, six-degrees-of-freedom (6DOF) tracker that is immune to cockpit and helmet scatterers of magnetic/electrical field energy, vehicle vibration, and harsh lighting conditions. Magnetic and inertial tracking technologies each have limitations that make them undesirable as next-generation solutions. Optical tracking technologies, while having occlusion problems, are increasingly seen as the more attractive next-generation solution. The optical tracker, developed at Ascension Technology Corp to meet these needs, measures the angle of incidence of point radiating emitters mounted on the helmet. The sensors measure angle of incidence in one dimension; two or three sensors are required to be mounted on the cockpit instrument panel to determine the position and orientation of the helmet. The sensor uses a transmissivity mask, which is located a known distance above a linear detector array surface. The mask consists of three transmissivity frequencies varying in one dimension. Each point radiating emitter illuminates the mask to cast an image onto the array. The array image is read at a high update rate and a remote processor identifies image phases to determine the image shift along the detector array axis. The three frequencies, being sufficiently separate in frequency to determine a coarse absolute image shift, as well as medium and fine image shifts, are used to determine a high-resolution absolute image shift. The image shift of each sensor is used to compute the plane angle of incidence of each emitter. The minimal system configuration includes two sensors and four emitters or three sensors and three emitters. More sensors and emitters may be used to increase tracker motion box. Flight tests were conducted in August and September of 2005. The phasorBiRD (trademark) prototype was flown in a test aircraft to evaluate the effect of direct sunlight and vibration on accuracy and noise.