Three-dimensional dynamic imaging of sand particles under wheel via gamma-ray camera system

In recent years, attempts have been made to deploy robots for use in various activities such as planetary exploration, post-tsunami seashore reconnaissance, and volcano investigations. These robots may have to move on soft terrain. The movement of sand or soil particles under the wheels or tracks greatly affects the robot's ability to maneuver. There is a simple but difficult problem with measuring particle movement: the sand and soil particles beneath the surface are not visible. Only 2D visualization techniques that take a surface picture of the ground or use transparent boards are available. A nuclear 3D imaging technique called positron emission particle tracking (PEPT) was developed at the University of Birmingham for this purpose. PEPT detects pairs of gamma rays emitted by a positron-emitting radionuclide of a tracer particle, which produces an image of the tracer. Thus, the overarching goal of this study was to explore the 3D terramechanics between terrain particles and a wheel or track using PEPT. As an initial step, this paper introduces an imaging technique for standard sand under a rotating wheel using PEPT and presents some images of sand particles under various conditions. Absolute displacements along the longitudinal, vertical, and lateral axes are presented.