To provide robots with a flexibility of operation, it is necessary to develop a sensor which can recognize the distance to the object as well as its surface shape. This paper investigates the robot sensor using the ring pattern method, where a circular pattern is projected on the object and the location and the shape of the object is recognized by analyzing the distortion of the projected pattern. In the proposed system, a conical beam is projected from a ring projector, and by varying the azimuth angle of the cone, both the distance and the shape are recognized. The distance to the object is determined utilizing the geometrical relation when the beam is focused to a point on the object surface. For the shape, the ring pattern is approximated by ellipses, and the shape is analyzed by the distributions of this parameter. The three‐dimensional data are obtained from the distortion of the projected pattern from the circle, which would have been obtained by projecting the light on a plane which is parallel to the projector plane and passing through the point of the measured distance. The measurement is made by scanning the beam on the object, and the result of recognition for the whole object is represented by the surface patching. An experimental system was constructed based on the proposed principle, using 6 projectors. A satisfactory result was obtained for the measurements of distance, shape and inclination of the plane. Using a book as the object, a grid scanning is made and the result is represented by the surface patching. It is seen that the edge and the curve of the paper can be recognized.
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