Tracking laser interferometer

A method of continually tracking a moving object relative to X and Y axes which are perpendicular and intersect at a point A at a reference location, comprising the steps of

• rigidly coupling a retroreflector to the object,
• directing a laser beam along the Y axis towards the X axis,
• redirecting the laser beam from the Y axis, before the beam intersects the X axis, along the X axis,
• redirecting the laser beam from the X axis at point A along an R axis incident on the retroreflector, the R axis being substantially perpendicular to the X axis and intersecting the X and Y axes at point A,
• generating an error signal from the displacement of the laser beam after incidence of the laser beam on the retroreflector representing movement of the retroreflector and object relative to the X and Y axes, and
• relocating the R axis relativ to the retroreflector and object so as to reduce the error signal to zero.

A tracking system for continually tracking a moving object relative to a reference location, the combination comprising:

• a retroreflector rigidly coupled to the object;
• a rigid stationary base positioned at the reference location;
• a first support;
• means for pivotally coupling said first support to said base for pivotal movement about a Y axis;
• a second support;
• means for pivotally coupling said second support to said first support for pivotal movement about an X axis, said X and Y axes being substantially perpendicular and intersecting at a point A;
• means for generating a laser beam directed along said Y axis towards point A;
• first reflective means, rigidly coupled to said first support, for receiving the laser beam extending along said Y axis before it intersects the X axis and redirecting the laser beam along said X axis towards point A;
• second reflective means, rigidly coupled to said second support, for receiving the redirected laser beam along said X axis from said first reflective means and redirecting the laser beam at point A along an R axis incident on said retroreflector;
• said R axis being substantially perpendicular to said X axis and intersecting said X and Y axes at said point A;
• motive means, coupled to said base and said first and second supports, for pivoting, respectively, said first and second supports relative to said base;
• detection means, located along the path of the laser beam, for receiving the laser beam after incidence on said retroreflector and for generating an error signal representing movement of said retroreflector and object relative to said X and Y axes;
• and
• control means, coupled to said motive means and receiving said error signal, for actuating said motive means to reduce said error signal to zero.