Interferometer system for controlling non-rectilinear movement of an object

An apparatus for controlling the movement of an object through a predetermined non-rectilinear path in a predetermined volume having X, Y and Z axes, the combination comprising:

• a support;
• a first means, coupled to said support and the object, for moving the object simultaneously along the X, Y and Z axes;
• a retroreflector rigidly coupled to the object;
• a housing rigidly coupled to the support and in a fixed position relative to the predetermined volume;
• first, second and third laser interferometers rigidly coupled to said housing, and having first, second and third laser output beams, and first, second and third output signals;
• first, second and third tracking mirrors, each associated with one of said laser interferometers for directing the associated laser output beam incident on the center of said retroreflector;
• second means for pivotally coupling each of said tracking mirrors to said housing for pivotal movement about two perpendicular axes;
• motive means, coupled to each of said tracking mirrors and said housing, for moving each tracking mirror to maintain each of said output beams incident on the center of said retroreflector;
• and
• control means, containing the X, Y and Z spacial coordinates of the predetermined path, coupled to said first means and said motive means and receiving said interferometer output signals, for
• (a) repeatedly determining the actual location of the object based on said interferometer output signals,
• (b) repeatedly comparing the actual location with the desired location along the predetermined path,
• (c) actuating said first means to move the object from its actual location to the next desired location along the predetermined path, and
• (d) actuating said motive means to pivot said tracking mirrors to maintain said laser output beams incident on the center of said retroreflector.