Optics: measuring and testing – Range or remote distance finding – Triangulation ranging to a point with one projected beam
Reexamination Certificate
2001-05-04
2002-04-09
Tarcza, Thomas H. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
Triangulation ranging to a point with one projected beam
C356S003050
Reexamination Certificate
active
06369879
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains generally to methods for determining the position and surface contours of an object and, more particularly, to a method for determining surface coordinates by directing intensity modulated illumination toward the surface of an object and identifying the source of the modulated illumination from the detected modulation pattern, whereupon the object coordinates may then be determined by triangulation.
BACKGROUND OF THE INVENTION
There are numerous applications that require a determination of the coordinates of the surface of an object, or the coordinates of reflective elements beneath that surface. Typical application areas include industrial plants, laboratories, microscopy, and the metrology field in general. Various optical methods have been employed that utilize arrangements of light sources to detect contour information. These methods are often employed within instruments such as coordinate measuring machines, three-dimensional topometric sensors, and laser triangulation sensors.
One common method of performing surface coordinate measurements is to project a lighted grid of lines onto the surface of an artifact, capture the reflected image on an image sensor, and then analyze the image data. The distortion of the grid within the image may be analyzed to discern the shape of the object. The grid lines may be mapped to ascertain the angles of the beams and the coordinates of the points of intersection. Triangulation is typically utilized during the process of calculating the coordinates of the object surface once sufficient angle and position data is obtained.
It will be appreciated that a right triangle can be resolved given any two sides, or an angle and a side.
FIG. 1
is a two-dimensional diagram of triangulation being performed to resolve the position of point P′, wherein a ray of light from a known location P and direction &thgr; is reflected from the surface of the object at point P′ and is detected at a location P″. A pair of right triangles is formed that may be solved for the coordinates of location P″ once the distance or additional angular information is known.
Methods of determining object coordinates often rely on a method of scanning the surface of the object point-by-point or line-by-line, and resolving the point positions of the object serially. However, sequential methods of plotting the coordinates of an object surface are slow and not well suited for use on vibrating or moving objects. The coordinates of object points may also be determined by creating interference patterns in the region near the surface using multiple illumination sources, such that the reflected patterns disclose changes in field depth as a series of interference fringes.
In another method, predetermined displacements of a projected light grid having a sinusoidal pattern are mechanically generated, as by rotating an aperture. The reflected light from the object is detected by an image sensor so that the response to the angular displacement for the aperture is evaluated by a phase-shift method (or Fourier transform) to determine the incoming angle of the light. The object location is then solved by triangulation. The two grating positions may be generated simultaneously using multiple wavelengths of light, such as colors in the visible spectrum, which are resolved by a detector individually responsive to each of the wavelengths. The utility of this technique and its accuracy are dependent on the surface characteristics of the object and require substantial precision with regard to the gratings and their rotation.
The aforementioned methods of determining the coordinates of an object surface suffer from a number of drawbacks, such as being typically slow, while many of the methods inherently lack mathematical precision. Therefore, a need exists for an efficient method of determining object position under a variety of conditions and which does not rely on image distortion, sequential scanning, interference patterns, or pixel position rotations. The present invention satisfies those needs, as well as others, and overcomes the deficiencies of previously developed solutions.
Various objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
SUMMARY OF THE INVENTION
The present invention is directed to an apparatus for determining the coordinates of points on the surface of an object. A modulated light source has pixels whose light intensity may be individually modulated, wherein the light source is directed toward the object. An image detector has a plurality of pixels for receiving light reflected from the surface of the object. Then, a computer, or the like, determines the coordinates of points on the surface of the object wherefrom pixels of light are reflected from the surface of the object, wherein the determination is responsive to the relative location of pixels registered on the imaging detector such that a sequence of intensity values detected by pixels of the image detector are correlated with a unique signature of light intensity values transmitted by pixels of the light source from which the location of the associated point of reflection from the surface of the object may be determined by triangulation from known locations of the image detector pixels and light source pixels.
Accordingly, the invention is a simplified method for determining the location of the points on the surface of an object by varying, in accord with a unique sequence, the intensity of each illuminated pixel directed to the object surface, and detecting at known detector pixel locations the intensity sequence of reflected illumination from the surface of the object whereby the identity and location of the originating illuminated pixel can be determined.
Various features of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.
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Osten et al., “General Hierarchical Approach in Absolute Phase Measurement,” SPIE vol. 2860, pp. 2-12.
Andrea Brian
Tarcza Thomas H.
The Regents of the University of California
Wilson Ray G.
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