| 摘要 |
A gauge for measuring small changes in the contour of the surface of a moving part, such as a rotating cylinder or sliding flat surface, as the part passes a point, using a monochromatic source of coherent light is disclosed. The gauge is based on the fact that the size and rate of movement of the speckles of a speckle pattern (formed by coherent light focused onto a nonspecular moving surface) vary in accordance with whether or not the beam is actually focused on the surface. In the preferred form of the present invention, an expanded and collimated laser beam is focused by a focusing lens onto the surface of the moving part. The speckle pattern light reflected by the moving surface is received by one or more photodetectors. The photodetectors develop pulses at a rate determined by the rate of speckle movement. These pulses are applied to a signal processor that counts them, if they are above a predetermined level. Pulse counts are made over predetermined time periods; and, if speckle size, as well as speckle rate is used as the measurements basis, only pulses occurring simultaneously on the outputs of two photodetectors are counted. The pulse counts made during adjacent time periods are analyzed by a signal processor and, then, compared. The results of the comparisons are used to control the focusing lens such that the coherent beam is brought to, and maintained in, focus on the surface of the part. Focus exists when the pulse count is maintained at a maximum level. The focusing lens position is denoted by an indicating scale mechanism, which provides the displacement information needed to determine the size of changes in the contour of the surface that cause refocusing of the focusing lens.
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