Optics: measuring and testing – Velocity or velocity/height measuring – With light detector
Patent
1995-06-15
1997-06-03
Buczinski, Stephen C.
Optics: measuring and testing
Velocity or velocity/height measuring
With light detector
324175, G01P 336
Patent
active
056360142
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. BACKGROUND OF THE INVENTION
The invention relates to a method and apparatus for determining the rate of rotation of a rotating object comprising directing a parallel beam of electromagnetic radiation towards the rotating object, detecting speckles from the object surface, and determining the transit times of the detected speckles.
The Technical Field of the Invention
The method and apparatus according to the present invention is useful for determining the rate of angular rotation, particularly the instantaneous rate of angular rotation, of a wide number of rotating objects having surfaces with predominantly one major specularly reflective component, e.g. objects such as rotating shafts of machined metal surfaces optionally polished, non-polished, painted, or covered with reflecting tape.
In the context of the present invention, the expression "rate of angular rotation" is intended to designate the instantaneous rotational velocity d.o slashed./dt measured as the time dt it takes a surface element to rotate a given angle d.o slashed.. Further, the expression "speckle" is intended to designate a detected speckle pattern of granular bright and dark spots produced by constructive and destructive interference between scattered specular and non-specular reflections from coherently irradiated irregular surfaces; the expression "objective speckles" is intended to designate speckles formed directly within the solid angle of the detection means; and the expression "subjective speckles" is intended to designate speckles obtained by optically transforming objective speckles. Speckles move dynamically as the surface of a continuous rotating object rotates.
Prior Art Disclosures
(a) Techniques Based on Objective Speckles
For the purpose of studying the dynamics of speckles produced in the near and far diffraction fields of rotating objects various methods for the determination of radius of curvature, angle of rotation, and speckle correlation have been disclosed in the literature.
Takai et al., Appl. Phys., B26, 185-192, (1981) disclose a method of real time measurement of the radius of curvature of a rotating diffuse object based on the time correlation length of the speckle intensity fluctuation produced in the Fresnel (near) diffraction field.
J. C. Marron and K. S. Schroeder, Applied Optics, Vol. 27, No. 20, 4279-4287, (1988) disclose a method of measuring correlations of dynamic speckles from rough rotating objects in which the speckle pattern, being translated perpendicularly to the object's axis of rotation, decorrelates depending on the amount of object rotation, locations of the source and observation planes, and the shape of the object.
Hayashi and Kitagawa, Applied Optics, Vol. 22, 3520-3525, (1983) disclose a method for measuring the rotation angle of a cylinder, particularly a small rotation angle with high resolution based on the speckle displacement detection in the (near) diffraction field caused by the cylinder surface rotation. The light intensity distributions of speckles before and after the cylinder surface displacement are detected by a detector array, and displacement of the speckle pattern is measured by computing their cross-correlation function. The distance to the cylinder surface and the radius of the cylinder have to be known.
In the above-mentioned articles nothing is indicated or suggested about dynamic measurements of rate of rotation.
Erdmann and Gellert, J. Opt. Soc. Am., Vol. 66, No. 11, 1194-1204, (1976) disclose studies of the effect of rotation and shape of objects with rotational symmetry on the speckle field of laser light scattered by such objects. The space-time correlation functions of the optical field and the intensity are calculated for moving objective speckles in the far field zone of symmetrically curved rotating surface of Gaussian roughness. It is found that the correlation function of the intensity depends on the radius of the incident beam, the local surface velocity and the radii of curvature in the illuminated region. Particularly, the cr
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Buczinski Stephen C.
Forskningscenter RIS.O slashed.
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