Optics: measuring and testing – Shape or surface configuration
Reexamination Certificate
2000-11-27
2001-12-04
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Shape or surface configuration
C356S602000, C356S608000, C356S612000, C356S127000, C356S237100, C250S559220
Reexamination Certificate
active
06327041
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and a device for opto-electrical acquisition of shapes.
2. Brief Description of the Prior Art
A number of techniques for opto-electrical acquisition of shapes are known in the art:
stereovision consists of deducing the relief of a surface by comparing images of the surface captured at two different angles at least; this method requires very large computing means, is limited to parts of the surface that are visible from both angles at the same time, and the location of edges is imprecise,
observation of a surface by a video camera whose focussing is varied, which associates a distance (the focussing distance) with each clear area of an image of the surface; this system requires very large computing means, the measurement times are long and the spatial resolution is not very good,
measuring the time taken by a light pulse to travel the distance between an emitter and the surface and between the surface and a receiver, or measuring the phase shift between modulated illumination projected onto the surface and the observed light backscattered by the surface; these means acquire points and must be associated with scanning means, which limits the acquisition speed,
triangulation determines the length of the two sides of a triangle when two angles of the triangle and the length of the third side are known, and one application of triangulation consists of projecting a structured light flux onto the surface, using a video camera to observe the deformations of the flux by the surface and deducing therefrom, by triangulation, the distances of points on the surface relative to a reference plane; this technique suffers the limitations of triangulation (it requires the largest possible distance between the illumination means and the video camera and different illumination and observation directions), with the result that complex surface areas cannot be illuminated and observed simultaneously.
SUMMARY OF THE INVENTION
An object of the invention is a new technique for acquiring a three-dimensional shape by optical means which does not have the drawbacks of the prior art techniques referred to above.
Another object of the invention is a technique for acquiring a three-dimensional shape by optical means which combines accuracy, speed and the capacity to observe complex shapes without shadow areas.
The invention thus provides a method of opto-electrical acquisition of the shape of a surface, consisting of illuminating the surface, capturing the light reflected or backscattered by the surface in a given direction, analyzing it and deducing from it the distances of points of the surface relative to a reference plane, characterized in that it consists of illuminating said surface with a plurality of light beams having different wavelengths and which converge on an axial illumination direction at different points distributed along that direction, capturing the light reflected or backscattered by at least one point on said surface illuminated by at least one of the aforementioned beams, spectrally analyzing the light captured and deducing from its spectral composition the distance of the aforementioned point relative to the reference plane.
The invention therefore determines the distance of a point relative to a reference plane simply and quickly by determining the spectral width and/or the center wavelength of the light reflected or backscattered by that point.
The illumination wavelength can be varied continuously between two limit values, for example. It can instead be varied discontinuously and assume a number of predetermined values.
The illumination beams preferably converge onto the axial illumination direction at points which are distributed along that direction in the order of the wavelengths.
The light reflected or backscattered by said surface is advantageously captured in a direction which is approximately coincident with the axial illumination direction. The method according to the invention is then not limited by “shadow areas” of the observed surface.
The illumination beams can have a circular cross section for determining the distance of a point element or quasi-point element of the illuminated surface or can be flat light beams which intersect along parallel lines substantially perpendicular to the axial illumination direction for determining the distance of a profile of the illuminated surface defined by the intersection of the surface and a plane passing through the axial illumination direction and parallel to the lines of intersection of the flat light beams.
The invention also provides a device for acquiring the three-dimensional shape of a surface, this device including means for illuminating the surface, means for capturing the light reflected or backscattered by said surface in a given direction, and means for analyzing the captured light, associated with information processing means for determining the distances of points of the surface relative to a reference plane, characterized in that:
the illumination means generate a plurality of light beams having different wavelengths and converging on an axial illumination direction at different points distributed along that direction,
the means for analyzing the light reflected or backscattered by said surface include spectral analysis means, and
the information processing means determine the distances of points of said surface from the spectral composition of the light analyzed.
To form the aforementioned light beams, the illumination means can include a polychromatic light source of particular spectral width, associated by means of a slit or a diaphragm with a dispersive element such as a prism, a grating or a holographic lens, for example, or the illumination means include a plurality of light sources of small spectral width and having different center wavelengths.
The spectral analysis means include a spectral dispersion element such as a prism or the like associated with photosensitive sensors in a linear or matrix arrangement.
The spectral analysis means include a triple linear strip of photodetectors for measuring and comparing light fluxes of three primary colors.
In a preferred embodiment of the invention, the spectral dispersion element of the illumination means is a chromatic lens whose focal length is varied continuously as a function of the wavelength and which is associated with an enlarging objective, for example an a focal objective, to increase the usable depth of field. The device further includes an objective for illuminating the surface with the aforementioned beams and capturing the light reflected or backscattered by that surface, the objective being associated with a mask or diaphragm including a circular orifice or a slit through which the light passes delimiting an observation area of the illuminated surface, and control means for relative displacement of the surface and the mask or diaphragm.
Generally speaking, the invention acquires a three-dimensional shape precisely, quickly and completely using relatively small computing means and relatively inexpensive optical means.
REFERENCES:
patent: 3843227 (1974-10-01), Kato et al.
patent: 4585349 (1986-04-01), Gross et al.
patent: 4674883 (1987-06-01), Baurschmidt
patent: 4900940 (1990-02-01), Nakamura
patent: 5054926 (1991-10-01), Dabbs et al.
patent: 5165063 (1992-11-01), Strater et al.
patent: 5168327 (1992-12-01), Yamawaki
patent: 5606174 (1997-02-01), Yoshimura et al.
patent: 5608529 (1997-03-01), Hori
patent: 5701173 (1997-12-01), Rioux
patent: 5745236 (1998-04-01), Haga
patent: 5880846 (1999-03-01), Hasman et al.
patent: 5889276 (1999-03-01), Yonezawa et al.
patent: 706027A (1996-04-01), None
Patent Abstracts of Japan, vol. 96, No. 1, Jan. 31, 1996.
JP 07.248211A (Toyota Central Research & Development Lab Inc.), Sep. 26, 1995.
Dentalmatic Technologies Inc.
Font Frank G.
Laubscher Lawrence E.
Nguyen Sang H.
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