ROTATION MEASUREMENT TECHNIQUES

AN ELECTRO-OPTICAL TECHNIQUE FOR THE MEASUREMENT OF RELATIVE MOTION BETWEEN COMPONENTS WITH ARC-SECOND ACCURACY IS PROPOSED. THE MEASUREMENT RANGE IS FUNDAMENTALLY UNLIMITED, QUITE PRACTICAL OVER SEVERAL DEGREES, AND PERMITS TRANSLATIONS IN EXCESS OF ONE INCH BETWEEN COMPONENTS. TWO APPLICATION ARRANGEMENTS ARE DISCUSSED. THE FIRST IS THAT OF TWO (OR MORE) SHAFTS ROTATING WITH RESPECT TO A STABLE REFERENCE. BY SENSING THE TANGENTIAL MOTION OF THE SHAFT SURFACES THE ROTATIONAL ANGLE IS KNOWN THROUGH THE SHAFT RADIUS IN A MANNER FREE FROM ERRORS DUE TO DEFECTS SUCH AS SHAFT WOBBLE OR ECCENTRICITY. THE SECOND IS THAT OF TWO PARALLEL FLAT SURFACES WHICH CAN ROTATE AND TRANSLATE WITH RESPECT TO EACH OTHER IN THEIR RESPECTIVE PLANES. THE PROPOSED TECHNIQUE WILL ALLOW THE ROTATION MEASUREMENT TO BE UNCOUPLED FROM THE TRANSLATION. BOTH APPLICATIONS EMPLOY THE OPTRA TWO-FREQUENCY LASER AND UTILIZE A TECHNIQUE BY WHICH THE MOTION OF A SURFACE ONTO WHICH A INTERFERENCE PATTERN IS PROJECTED PRODUCES A MODULATION OF THE AMPLITUDE OF THIS FRINGE PATTERN FROM WHICH CAN BE INFERRED THE MOTION OF THE SURFACE.