Importance

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Abstract

An optical technique for determining remotely movement of a movable point such as a point on a robotic end effector moving in three-dimensional space, based on observation of moving fringe patterns. In a preferred embodiment, at least one moving interference fringe pattern is projected from at least one spaced pair of coherent point light sources, having different frequencies, and a photodetector responsive to illumination at the movable point is employed to count fringes as they cross the movable point. The difference frequency between the light sources causes the fringes to move at a known rate to provide sense-of-direction information in that this results in the detector output having a frequency component which reflects point motion. Full three-dimensional location is obtained by observing three independent fringe patterns in three independent directions. Such a set of patterns can be produced by as few as three point sources operating at three different frequencies. All three fringe patterns are followed with a single detector, provided the frequency shift introduced for each pattern is substantially different. Thus, if these shifts are represented by .delta..sub.1, .delta..sub.2, and .delta..sub.3, the detector signal can be filtered at corresponding frequencies to separate that part of the signal corresponding to each pattern. This frequency multiplex technique works unambiguously providing .delta..sub.1, .delta..sub.2, and .delta..sub.3, and all differences between these quantities are much greater than frequency shifts introduced by point motion.

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First Claim