Abstract: Speckle pattern interferometry using phase stepping anddigital processing is proposed and has been used tomeasure the shape and deformation of a 3D surface. Afour beam arrangement, in which one beam is chosen toact as a reference beam, is described. A low costpiezo- electric translator is incorporated in thearrangement to permit the implementation of phase-stepping. Images are acquired by a CCD camera and PCbased image processing system. As well as providing 3Ddeformation measurements, the arrangement has also beenused to determine the object shape by moving one of theilluminating beams. For the shape and deformationmeasurements, 13 independent speckle patterns areacquired and processed. Phase maps are produced using aconventional 3-step technique and hence surfacecontours, displacements, and strains can be obtained. Aspeckled object-reference beam is used and has theadvantage that the measurements are less sensitive tovibration and whole body motion than a smooth referencebeam arrangement. A flat surface mounted in proximityto the surface under investigation acts as a referenceplane and is used to improve the accuracy of themeasurements by validating the phase-stepping steps andverifying geometric and sensitivity parameters. Thetechnique has been applied to the measurement of acylinder under internal pressure. The experimentalresults are compared with conventional pointmeasurements. The optical arrangement and experimentalmethodology are described. Advantages and limitationsof the technique, together with sources of error andmeasurement uncertainties are discussed.!5
展开▼
