A realtime 3D measurement system of moving objects using laser beam scanners

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Principle of Measurement : A laser beam scanner scans a vertical slit beam by 360Hz across a huge field, where objects (athletes) with an optical reflector are moving around. Reflected beam from moving objects is detected by a position sensing device (PSD), which determines the exact time of reflection representing horizontal angular position of the object. The vertical angular position is determined by the position output of the PSD.A statistical method and interpolation were empolyed to determine accurate coordinates of objects.Achievements : A semiconductor laser (4w, 812nm) was used as the light source, and an aberration free lens was used to generate a rectangular beam (2mx0.2m). The beam splitter in the former model to separate the reflected light from the incident beam was replaced by a mirror with a small hole for the incident light to get through, which dramatically improved the sensitivity of the photo detector, together with a specially designed camera lens with a small aperture number. An interference filter was also employed to reject all of background illumination other than the laser light, which allowed to eliminate influence of daylight or electric illumination.Measurement noise proved to be 0.15mm in horizontal and 0.25mm in vertical directions, when measurement is done at a posidion 20m from an object, and 0.55mm at a position 50m from an object. In 3D measurement, measurement noise in near and far direction was estimated as less than 0.26mm at 20m, and 0.95mm at 50m.For the sake of laser light, the cross section of the beam at the surface of the polygon could be much less than the former model (Xe lamp was used as the light source), allowable scanning angle was increased by 30% (from 58deg to 75deg), resulting the size of measurement area being 30mx2m at 20m position, and 75mx2m at 50m position.A simulation was done to prove that 10 moving objects and a reference still object positions could be determined in realtime.