Distributed optical proximity sensor system: HexEYE

HexEYE is a novel optical proximity sensor system designed and evaluated for robotic applications, and capable of measuring the distance to and the orientation and curvature of a local area of object surface. The system derives its name (short for "hexagonal eye") from its shape: seven identical hexagonal sensing units are configured hexagonally into a compact geometric structure, as shown in Figure 1. Each sensing unit consists of six linear receiver arrays installed on each side of the hexagonal prism, a conical mirror located inside the prism, and a light source positioned at the center hollow of the conical mirror. Figure 2 shows the detailed layout of a single sensing unit. The light flux scattered from the light spot generated by the laser diode is collected by the objective lens and this image is then projected onto the receiver arrays by the conical mirror. The target distance is then measured based on the location, size, and shape of this image. HexEYE's seven sensing units are grouped into multiple combinations of three called Orientation Measurement Units (OMUs), which measure surface orientation as well as curvature. In distance measurement mode, the seven light sources are activated one at a time to generate a light spot on the target surface, while all sensing units receive the light flux scattered from the same light spot and contribute to the measurement. The orientation is measured through each OMU defining the local area by the three light spots which it generates. The final decision of the orientation or curvature of local surface area is based on integrating the six orientation measurements from six OMUs.

HexEYE has the following distinctive features:

1. It achieves an order of magnitude increase in distance sensitivity by optimizing the curvature of the conical mirrors, thus extending the measurement range for a given sensor size.

2. It provides enhanced measurement accuracy based on multiple levels of sensor fusion: The first level occurs at a single sensing unit, where the distance measurement is based on the data from six individual receiver arrays. The second level occurs when multiple sensing units are used for the distance measurement, where two sources of distance measurerment (based on Gaussian lens law and triangulation) are combined. The third occurs in the decision on surface orientation or curvature, based on multiple OMUs.

3. It is compact (l"diameter by 1- 1/4,"length), due to the sensing mechanism (based on Gaussian lens law) and the image projection (based on the conical mirror). A prototype of a single sensing unit has been built with commercially available parts and evaluated experimentally.

This invention is owned by NASA with a U. S. Patent, No. 4893025. More details can be found in RA Distributed Proximity Sensor System: HexEYE,S Proceedings of the 1992 IEEE International Conference on Robotics and Automation, May 1992, Nice, France.

Point of Contact:
Sukhan Lee
Mail Stop 198-219
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
818-354-2013
Sukhan.Lee@jpl.nasa.gov

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