Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2002-07-24
2004-11-23
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
C356S450000, C356S479000, C356S485000, C356S487000, C356S491000, C356S495000
Reexamination Certificate
active
06822746
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an interferometric measuring device for measuring the shape of a surface of an object. The present invention includes a radiation source emitting a short-coherent radiation, a beam splitter for forming an object beam directed at the object via an object light path and a reference beam aimed at a reflective reference plane via a reference light path. The present invention also includes an image converter which picks up the radiation reflected back from the surface and the reference plane and brought to interference and sends it to an analyzing device for determining a measurement result pertaining to the surface. For the measurement, the optical length of the object light path may be varied relative to the optical length of the reference light path or scanning of an intermediate image of the surface generated in the object light path may occur.
BACKGROUND INFORMATION
A conventional interterometric measuring device is described in German Published Patent Application No. 41 08 944 which is based on the measuring principle of white-light interferometry or short-coherence interferometry. According to the measuring principle, a radiation source emits short-coherent radiation which is split by a beam splitter into an object beam which illuminates a measuring object and a reference beam which illuminates a reflective reference plane in the form of a reference mirror. To scan the object surface in the depth direction, the reference mirror is moved in the direction of the optical axis of the reference light path by a piezo control element. When the object light path corresponds to the reference light path, the maximum interference contrast is obtained in the area of the coherence length and is detected by a photoelectric image converter and a downstream analyzing device and is analyzed on the basis of the known deflection position of the reference mirror to determine the contour of the object surface.
Additional such interferometric measuring devices and interferometric measuring methods based on white-light interferometry are described by P. de Groot, L. Deck, “Surface profiling by analysis of white-light interferograms in the spatial frequency domain” J. Mod. Opt., Vol. 42, No. 2, 389-401, 1995 and Th. Dresel, G. Häusler, H. Venzke, “Three-dimensional sensing of rough surfaces by coherence radar,” Appl. Opt., Vol. 31, No. 7, 919-925, 1992.
A conventional interferometric measuring device based on white-light interferometry is also described in German Patent Application No. 199 48 813 (not published previously) wherein to perform measurements in narrow hollow spaces, lateral resolution is increased by producing an intermediate image in the object light path. German Patent Application No. 100 15 878.1, likewise not published previously, proposes scanning of an intermediate image to increase the depth of focus with a relatively high lateral resolution at the same time.
There may be problems with the conventional interferometric measuring devices and measuring methods if the measurement task requires scanning of several separated surfaces which are several millimeters apart, for example, and/or are oriented at an inclination to one another.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an interferometric measuring device with which at least two spatially separated surfaces may be measured with accurate and highly reproducible measurement results.
In addition to producing an image of the one surface, an image may be produced of at least one other surface. This may be achieved in the following manner. At least one additional reference plane which is used for depth scanning may be situated in the reference light path according to the number of additional surfaces for generating different optical lengths in the reference light path. The radiation reflected back by the minimum of one additional surface and the respective additional reference plane and also brought to interference and scanned for the measurement may also be sent to the image converter and may be analyzed in the analyzing device for determining the measurement result.
For example, with superposition optics or optics having a corresponding depth of focus, it may be possible to detect and image simultaneously multiple separated surfaces of the same object or different objects, e.g., a guide bore and a valve seat. Splitting the reference light path into partial reference light paths having optical lengths adapted to the different surfaces to be measured may permit simultaneous scanning or scanning in short intervals and therefore rapid scanning of the interference peaks of the various surfaces, for example. The interfering radiation of the various surfaces may be picked up by the image converter simultaneously or in succession and sent to the analyzing device for deriving measurement results, e.g., the position of the various surfaces relative to one another, the height and parallelism and/or the properties of the various surfaces themselves. This may simplify the handling and design of the measuring device.
Configuration options include a superposition optics being situated in the object light path, permitting generation of an image of the one surface and the minimum of one additional surface. Another option is for the additional surface to be imaged on the image converter either directly or via at least one intermediate image in the object light path.
Two alternative exemplary embodiments of the reference light path include a side-by-side configuration or a series configuration of the reference plane and the minimum of one additional reference plane in the reference light path, the minimum of one upstream reference plane being partially transparent in the case of a series configuration. In the case of a side-by-side configuration, different optical elements may be contained in the different partial reference arms.
Different measurement options are obtained due to the fact that the one surface and the minimum of one additional surface belong to objects positioned simultaneously or in succession, the surface and the minimum of one additional surface being situated at different distances.
According to various exemplary embodiments, the object light path for generating a common intermediate image of the surface and the intermediate image of the additional surface(s) may be formed in a common intermediate image plane in the object light path, and the common intermediate image may be imaged on the image converter either directly or via at least one intermediate image. With at least one intermediate image in the object light path, it may be possible to scan an intermediate image and also to obtain an increased lateral resolution.
In accordance with other exemplary embodiments, the reference light path may be formed in a separate reference arm or in a measurement arm belonging to the object light path.
To measure different surfaces in hard to reach places, an optical system, that is rigid relative to the object, may be situated in the object light path, and the rigid optical system may be followed by an optical system that is movable in the direction of its optical axis.
An exemplary embodiment in which the object light path is designed as an endoscope may be advantageous for narrow cavities and a measurement having a relatively high lateral resolution.
The effort of adapting the measuring device to various measurement functions may be facilitated by arranging the rigid optics as part of the optics producing the intermediate image.
To achieve a robust measurement with respect to relative lateral movement of the object, the rigid optics may produce images toward infinity.
If an image of the reference plane or the additional reference plane is within the depth of focus range of the superposition optics, this may contribute to the accuracy of the measurement. It may be advantageous that the image of the reference plane and/or the additional reference plane lie in the plane of the image of the superposition optics, and in addition, with movement of the mobile
Lindner Michael
Prinzhausen Friedrich
Thominet Vincent
Brown Khaled
Font Frank G.
Kenyon & Kenyon
Robert & Bosch GmbH
LandOfFree
Interferometric, low coherence shape measurement device for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Interferometric, low coherence shape measurement device for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Interferometric, low coherence shape measurement device for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3343233