US 5,402,233 A · Furnace control apparatus using polarizing interferometer

Abstract

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.

Claims39

Dependent claims

Apparatus for controlling furnace type processes which heat generally opaque work subjected to random vibrations in an atmosphere controlled enclosure to impart desired physical and/or metallurgical properties to said work, said apparatus comprising:

means for generating a plurality of pulsed sound waves in said work at frequencies higher than said random vibrations;
and
means for sensing said sound wave in said work, said sensing mean including means for generating a light source beam;
initial beam splitting means for splitting said light source beam into a reference beam and a signal beam directed against work in the vicinity of but spaced from the source of said sound waves;
mirror means for collecting scattered light from said work as said signal beam and directing said signal beam onto a signal beam path and directing said reference beam on a reference path;
polarizing means for changing the state of polarization of at least one of said reference beam and said signal beam with at least one of said beams generally circularly polarized;
means to combine said signal and reference beams into a resultant beam;
photon detecting means for sensing light in said resultant beam and generating an electrical signal in response thereto indicative of the intensity and phase-shift between said signal and reference beams for each sound wave;
said mirror means including means to mount said mirrors in a non-rigid manner by which said signal and reference beam paths can vary, during furnace operation, by a distance as great as the coherence length of said detecting laser beam of anywhere from one to a few centimeters of length;
and
calibrating means for obtaining from said plurality of signals a plurality of electrical signals with characteristics of said sound wave, and in turn correlating said sound wave characteristics with said physical and/or metallurgical properties of said work whereby said process is directly controlled by non-destructively sensing properties of said work.

8 more elements

A system for regulating industrial processes by non-destructively sensing surface wave movement on a workpiece subjected to random vibrations, said system comprising:

a) a means for generating a plurality of pulsed sound waves in said workpiece at frequencies higher than said random vibrations;
b) polarizing interferometer means for recording surface movement of said workpiece in response to said sound waves by a plurality of electrical signals, said polarizing interferometer means including mirrors mounted in a non-rigid manner for developing a signal beam path and a reference beam path maintained equal to one another within the coherence length of light traveling on said paths of about one to several centimeters, said polarizing interferometer means including means for developing a reference beam from a probe light source and means for developing a signal beam at a fixed distance from said sound wave generating means from probe light reflected by said workpiece;
and
c) means for calibrating surface movement measured by said polarizing interferometer means from a subset of said electrical signals relative to a workpiece property.

1 more element

In an industrial furnace for heat treating metallic workpieces subjected to random vibrations to impart desired physical and/or metallurgical properties thereto, the improvement comprising:

a control system for non-destructively measuring said workpiece and regulating said furnace in accordance with said measurements, said system including
a) means for generating a plurality of pulsed, sound waves at frequencies higher than said random vibrations in said workpiece;
b) polarizing interferometer means for recording movement of the surface of said workpiece in response to said sound waves by a plurality of electrical signals, said polarizing interferometer means including mirrors mounted in a non-rigid manner for developing a signal beam path and a reference beam path maintained equal to one another within the coherence length of light traveling on said paths of about one to several centimeters, said polarizing interferometer means including means for developing a reference beam from a probe light source and means for developing a signal beam at a fixed distance from said sound wave generating means from probe light reflected by said workpiece;
c) means for correlating from a subset of said plurality of signals the surface movement of said workpiece with said property;
and
d) means for controlling said furnace directly in response to said surface movement.

3 more elements

Dependencies are inferred from the claim text.

Furnace control apparatus using polarizing interferometer

Life of this patent

Furnace control apparatus using polarizing interferometer

Life of this patent

Abstract

Claims39