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Apparatus for measuring surface movement of an object that is subjected to external vibrations

United States Patent

5,623,307
April 22, 1997
View the Complete Patent at the US Patent & Trademark Office
A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading.
Kotidis; Petros A. (Waban, MA), Woodroffe; Jaime A. (North Reading, MA), Rostler; Peter S. (Newton, MA)
Textron Defense Systems, Division of Avco Corporation (Wilmington, MA)
08/ 381,201
January 31, 1995
This invention was made with government support under contract no. DE-FC07-89ID12830 awarded by the Department of Energy. The government has certain rights in this invention.