Deformation measuring method and apparatus using electronic speckle pattern interferometry

Abstract

A deformation measuring method using electronic speckle pattern interferometry comprises the steps of subtracting an average intensity from the intensity in a time domain at each point of a speckle pattern image so as to compute the cosine component of intensity; subjecting the cosine component to Hilbert transform in a temporal domain so as to compute the sine component of intensity; determining the arctangent of the ratio between thus computed sine and cosine components so as to determine an object phase; carrying out an unwrapping operation; and outputting three-dimensional deformation distribution data in a displayable mode.

What is claimed is:  
     
         1 . A deformation measuring method using electronic speckle pattern interferometry, said method comprising the steps of determining a phase change curve of a dynamic object to be observed phase-wrapped in a predetermined phase range by analysis according to a speckle pattern image carrying phase information of said object obtained by using electronic speckle pattern interferometry; and then phase-unwrapping said phase change curve; 
 wherein, according to a plurality of speckle pattern images each obtained at a predetermined time, an intensity signal in a temporal domain of each image point is determined, a cosine component of said intensity signal is extracted, thus extracted cosine component is subjected to Hilbert transform in said temporal domain so as to determine a sine component of said intensity signal, and determine a phase change for each image point according to a ratio between thus determined sine and cosine components so as to determine a phase change curve of said object.    
     
     
         2 . A deformation measuring method according to  claim 1 , wherein said Hibert deformation is carried out by using the following expression:  
       
         
           
             
               
                 
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       where t and t′ are times, whereas f(t) is a function of time.  
     
     
         3 . A deformation measuring method according to  claim 1 , wherein a phase component ωt introducing a temporal carrier for monotonously increasing or decreasing a phase term of an intensity signal I(x;t) in a temporal domain for each image point is added to or subtracted from said phase term.  
     
     
         4 . A deformation measuring method according to  claim 3 , wherein said phase component ωt is added or subtracted by causing a piezoelectric transducer to move a mirror surface of a luminous flux reflecting mirror provided for one of two illumination luminous fluxes for generating speckle pattern interference so as to change an optical path length of said one illumination luminous flux.  
     
     
         5 . A deformation measuring method according to  claim 1 , wherein said dynamic object is a test piece subjected to a tensile test.  
     
     
         6 . A deformation measuring apparatus using electronic speckle pattern interferometry for determining a phase change curve of a dynamic object to be observed phase-wrapped in a predetermined phase range by analysis according to a speckle pattern image carrying phase information of said object obtained by using speckle pattern interferometry; and then phase-unwrapping said phase change curve; 
 said apparatus comprising: 
 intensity signal calculating means for determining an intensity signal I(x;t) in a temporal domain for each image point according to a plurality of speckle pattern images each obtained for a predetermined time;  
 average component eliminating means for subtracting a predetermined average intensity signal I 0 (x;t) from said intensity signal I(x;t) outputted from said intensity signal calculating means so as to compute a cosine component I c (x;t) of said intensity signal;  
 Hilbert transform operating means for subjecting said cosine component of said intensity signal outputted from said average component eliminating means to a Hilbert transform operation in said temporal domain so as to compute a sine component of said intensity signal; and  
 object phase determining means for carrying out an operation for determining an arctangent of a ratio between said cosine component of said intensity signal calculated in said average component eliminating means and said sine component of said intensity signal calculated in said Hilbert transform operating means so as to determine a phase change curve of said object.  
   
     
     
         7 . A deformation measuring apparatus according to  claim 6 , further comprising temporal carrier superposing means for superposing an appropriate temporal carrier onto the intensity signal I(x;t), said temporal carrier superposing means comprising optical path length difference generating means for generating a predetermined optical path length difference between two illumination luminous fluxes for generating speckle pattern interference.  
     
     
         8 . A deformation measuring apparatus according to  claim 7 , wherein said optical path length difference generating means is a luminous flux reflecting mirror configured such that a mirror surface thereof is movable with a piezoelectric device.