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Abstract

A photoplotter having a photohead that moves in one coordinate direction and a film table movable in another coordinate direction employs a dual-axis, single mirror and reflector interferometer system for measuring movement of the film and photohead relative to one another. The photohead is mounted on a bridge over the movable film table and a first interferometer mounted on the head cooperates with an elongated mirror at the edge of the table for measuring the relative position of the film and head in the first coordinate direction. Another interferometer mounted on the bridge cooperates with a retroreflector on the head to measure movement of the head relative to the film in the second coordinate direction. The two measurements from the interferometers are employed as feedback signals in a closed loop positioning system for the photohead and table.

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First Claim