The Minnesota Scanner: A Prototype Sensor for Three Dimensional Tracking of Moving Body Segments

An advanced method of tracking the three dimensional motion of bodies has been developed. This system, which is presently being used for human motion tracking, has the potential for dynamically characterizing robot motion and also provides a means for facilitating robot endpoint control. Three rotating planes of laser light, fixed and moving photovoltaic diode targets, and a pipelined architecture of analog and digital electronics are used to locate multiple targets whose number is only limited by available computer memory. Data collection rates are a function of the laser scan rotation speed and are currently selectable up to 480 Hz. The tested performance on a preliminary prototype designed for 0.1-in accuracy (for tracking human motion) at a 480-Hz data rate includes a resolution of 0.8 mm (0.03 in), a repeatability of ±0.635 mm (±0.025 in), and an absolute accuracy of ±2.0 mm (± 0.08 in) within an eight cubic meter volume with all results applicable at the 95-percent level of confidence along each coordinate direction. The system can be used to reduce XYZ target position data to body angular orientation which, for this first prototype, ranges in accuracy from ±0.5° to ±1°. Moving targets can be tracked at speeds exceeding 1 m/s with signal integrity tested but not limited to 25-Hz motions.