Flat Docking Target

A lenticular array of tiny lenses was designed and developed to enable the fabrication of a very thin (1mm) flat target device which still provides appropriate alignment cues to an operator when viewed through an end effector mounted camera. In order to provide a large viewing angle, the micro lenslets are shaped spherically. The design implemented for this research activity generates an apparent three-dimensional image from the whole array, with parallax in both x and y planar directions so that the operator perceives relative movement of the target pattern in all directions on approach. The prototype design uses a cross that is divided into three segments that appear to be at different depths. The inner portion of the cross appears to be closest to the viewing surface. The intermediate segment appears to be slightly below the closest image. The bottom outer segment appears to be at the greatest distance from the top image. When viewed over the center of the target, normal to the surface, the three segments line up to form a single cross. As the viewer moves off normal, the three portions appear to separate.

The difference in depth between the bottom and intermediate segments is fairly small, so that the relative motion is slight and only aids coarse alignment as the end effector camera approaches the target. The difference in depth between the intermediate and top segments is relatively large, so that the relative motion is sizeable for fine alignment. The optical arrangement used to put the pattern on the back of the lenslet array is a Fresnel lens with a 9-inch nominal focal length and a 10-inch aperture. The target is placed 13 inches from the Fresnel lens when the photosensitive backing is ex- posed. Multiple exposures for the three cross segments are made with a slit allowing light from a uniform light source to pass. The cross projected onto the target was 1/16-inch thick. The distances of the slits from the Fresnel lens were 39, 29, and 27 inches respec- tively causing the images to be nominally -1.11, .05, and .5 inches behind the target. In order to record the images on the back of the target, they are first coated with Liquid Light, a commercially available photographic emulsion and, after exposure, developed. After developing and drying, the back of the target is coated with Krylon white enamel to protect the emulsion and produce a reflecting backing.

Point of Contact:
Wayne Zimmerman
Mail Stop 198-219
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
818-354-0234
zimmerman@telerobotics.jpl.nasa.gov

Donald Gennery
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
818-354-0956

Telerobotics Program page

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Maintained by: Dave Lavery
Last updated: May 10, 1996