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US 2007/0165240 A1Published application
Shape measurement method
AssigneeCarl Mahr Holding GmbH
InventorPeter Lehmann
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AssigneeCarl Mahr Holding GmbH
InventorPeter Lehmann
Estimating the term…
An interferometric measuring method for detecting shapes is based on the interferometric observation of an object surface subjected to narrow-band lighting. A movement of the interferometer (1) relative to the object surface (2) generates a measuring signal on a suitable photo receiver, for example a camera circuit (5), from which two extremely closely positioned signal frequencies (f0) and (f0+Δf) are extracted. The phase difference between the two signal components is used for determining the distance and/or the change in the distance. The method has a large unambiguousness range, thus making it possible to have a large depth measurement range. The method can also be used for workpieces having offset areas on the surface, wherein the measurement is not disturbed along the edges and the offset areas of the body. The method also allows examining strongly inclined surfaces having an inclination that is steep enough, so that traditional methods based on generating and evaluating interference lines cannot be used because of an extremely high density of the interference lines.
A measuring method for detecting the deviation Δz of the distance z of at least one surface point (3) from an objective (4), wherein with this measuring method the light from at least one light source (12) is divided into a measuring beam and a reference light beam which, following reflection on the surface point (3), are again combined and cause interference on a photo receiver (5), wherein the length of the measuring light path (8) traversed by the measuring light beam, and/or the length of the reference light path (9) traversed by the reference light beam, are changed for realizing this measurement and wherein the photo receiver (5) meanwhile emits a time-variant measuring signal containing spectral components, of which at least two are extracted through a computer circuit (16) or by using a time offset and are used for determining the deviation Δz in that the respectively allocated phase angles φ1 and φ2 are determined from a set of scanning values (sm+mo) of the measuring signal for a first signal frequency f0 and for a second signal frequency f0+Δf, and wherein the deviation Δz is computed from this.
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