We propose a new method for vibration measurement in non-rigid test environment with electronic speckle pattern
interferometry (ESPI). The ESPI is useful for non-contact, real-time analysis of vibration. This method needs rigid test
environment, however. When the interferometer and a vibration surface are on a non-rigid table or their environments
are separated, especially at manufacturing areas, high-amplitude, low-frequency noise fluctuation overwhelms a
vibration signal and the amplitude fringes disappear. We use electronic shutter function of a TV camera and reduce
exposure time of an image sensor. With the time reduction, we may extract an image from many input images, during
whose acquisition time noise fluctuation turns back and its magnitude is so small that the vibration signal goes to be
included in the image. We accumulate the images and increase the contrast of the amplitude fringe map.
We evaluated usefulness of this method with circular saw vibration. The interferometer and the saw are fixed on a rigid
board and the noise fluctuation is electronically superposed on the vibration signal with sine wave. This method is
successful for a fluctuation amplitude of 60μm.
We propose a new method for measuring vibration frequency with electronic speckle pattern interferometry. In this method, laser beam wavelength is modulated with an independent frequency. In accordance with a frequency difference between the modulation and the vibration, a maximum intensity in a fringe pattern image changes. When the modulation magnitude is reduced, the frequency difference between the vibration and the modulation, in which the fringe pattern diminishes, widens and the maximum intensity in the fringe pattern image alters gently while the modulation frequency is scanned. Then we can search the vibration frequency, in which the maximum intensity in the image has a peak when the modulation frequency equals to the vibration frequency, with a hill-climbing method. It is confirmed in an experiment that the vibration frequency can be measured in a short time sufficient for practical use.
We propose a new technique of speckle interferometry which can measure a dynamic phase change in large deformation. In this method, we use a continuous tracking approach of the deformation we proposed previously, and apply a new technique, which can measure the large deformation by eliminating a noise term not correlating to the deformation, to the approach. A 450 μm in-line deformation of an aluminum plate was successfully tracked in an experiment.
We propose a new profile measurement system with light sectioning, which is available to detect step profiles on objects. We can intercept obstructive signals due to the day light reflected from the objects, by using a modulated laser beam and lock-in demodulation. The performance of this system was confirmed by experiments, in which step profiles of objects at a distance of 500 mm could be measured.
Resolution-variable moiré topography for measuring the three-dimensional profile of an object is described. With this method, moiré fringes are formed by projecting two sets of interference fringes of laser beams on an object. The interference fringes are formed using a Mach-Zehnder interferometer and are divided into two sets by a beamsplitter. The image, including the moiré fringes, which are formed in accordance with the object depth, is detected by an image sensor. The effectiveness of this method is demonstrated by practically measuring the profiles of a small object. The intervals between adjacent moiré fringes could be experimentally changed from 0.16 to 1.6 mm. The advantage ofthis method is that the interval between moiré fringes can be easily changed continuously by a mechanical operation.
The use of the phase shifting interferometric technique is discussed to make quantitative surface profiling
using the Nomarski differential interference microscope. Lateral shift of the Nomarski prism introduces
mutual phase shift between interfering two wavefronts with small amount of shear. Since the analyzed
phase distribution corresponds to the differential of the surface profile under test, integration of the phase
distribution gives the correct surface topography. The procedure for an analysis method and experimental
results are presented.