Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1992-03-02
1993-11-16
Rosenberger, Richard A.
Optics: measuring and testing
By polarized light examination
With light attenuation
250237G, G01B 1124
Patent
active
052628442
DESCRIPTION:
BRIEF SUMMARY
The invention relates to apparatus for determining the three-dimensional shape of an object optically and without contact, said apparatus comprising means for projecting a pattern on the object, which pattern includes fringes or lines with a light intensity that varies sinusoidally in space.
European patent EP 0 182 469, for example, describes the principle of determining the three-dimensional shape of an object by projecting onto the object a field of rectilinear fringes having a light intensity that varies sinusoidally in space, by forming an image of the object on photodetectors, and by measuring the phases of the signals from the photodetectors. To implement this principle, n fields of fringes are projected onto the object using a first pattern, with the fields being phase shifted by 2.pi.
from one field to the next, and then, using a second pattern, n fields of fringes having a different pitch are projected onto the object, which fields are likewise successively phase shifted by 2.pi.
, thereby resolving the 2k.pi. ambiguity (where k is an integer) in the phase measurements obtained using the first pattern.
In conventional manner, the field of rectilinear fringes may be in the form of a reversal film of the slide type on which a pattern of parallel lines is formed with the transparency of the slide varying sinusoidally in a direction perpendicular to the lines. Means are provided to displace said pattern transversely over n distances equivalent to phase shifts of 2.pi.
, and means are provided for changing the pattern, so as to remove the 2k.pi. ambiguity on phase measurement. The measurement must be performed in a time interval that is compatible with the intended application of this principle and which may be relatively short in some applications. The above-mentioned means for displacing and changing the pattern must therefore be as accurate, as rapid, and as reliable as possible.
An object of the invention is to provide apparatus of the above-specified type which satisfies said conditions.
To this end, the present invention provides an apparatus for determining the three-dimensional shape of an object optically and without contact, the apparatus comprising means for projecting the image of a pattern onto the object, the pattern comprising fringes or lines with a light intensity that varies sinusoidally in space, which patterns are formed, for example, on slide type reversal film, and cam means for displacing the pattern in a direction perpendicular to the optical axis of the projection means and perpendicular to the direction in which the fringes or lines of the pattern extend, the apparatus being characterized in that it comprises at least two patterns having fringes or lines at different pitches, which patterns are disposed in the same plane perpendicular to the optical axis and are carried by a moving support guided in translation in a direction perpendicular to the optical axis and parallel to the direction in which the fringes or lines extend, and motor means for driving said support in discontinuous reciprocating motion so as to center each pattern in succession on the optical axis.
This organization makes it possible to change very quickly the different-pitch patterns that must be projected on the object whose three-dimensional shape is to be determined, since this can be done merely by displacing a vertical support in translation over a relatively short stroke.
According to another characteristic of the invention, each pattern is connected to the moving support by two resiliently deformable parallel blades constituting guide means and return means urging the pattern in a direction that is opposite to the direction in which the cam means operate.
These means for mounting the patterns on the moving support then also constitute the means for guiding and returning the patterns, thereby simplifying both the structure and the operation of the apparatus of the invention.
According to yet another characteristic of the invention, the above-mentioned cam means comprise cams rotated about axes tha
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patent: 5003187 (1991-03-01), Zumbrunn et al.
Georgel Jean-Claude
Millet Jocelyn
Bertin & Cie
Rosenberger Richard A.
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