Importance

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Abstract

An apparatus is disclosed for determining the position of a moveable element over the surface of a solid medium. First and second transducer devices are provided and are moveable for placement at selected respective first and second locations on the surface for coupling with said surface. A third transducer device, for coupling with said surface, is mounted with the moveable element. Ultrasonic energy is transmitted, in either direction, between the third transducer device and the first and second transducer devices, the ultrasonic energy travelling through said solid medium. The transit times of the ultrasonic energy propagating, in either direction, between the third transducer device and the first and second transducer devices are determined, the transit times being indicative of the position of the third transducer device with respect to the first and second transducer devices. In a disclosed embodiment, the first and second transducer devices have tips that are feet of a housing and contact the surface over an area that is less than 2 mm.sup.2 and preferably, less than 0.5 mm.sup.2. A reflection reducer is provided at at least some of the edges of the solid medium.

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First Claim