Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1998-11-25
2001-10-02
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S201900, C250S206100, C356S121000
Reexamination Certificate
active
06297497
ABSTRACT:
The invention relates to a method and a device for determining the direction, defined by a horizontal and vertical angle, to an object which emits or reflects optical radiation, the radiation being picked up by an imaging optical system for producing an object image on a spatially resolving optoelectronic detector, the detector signals being fed to an evaluation device, and the direction to the object being determined from the coordinates of the object image on the detector.
The radiation coming from the object is intended to lie in the optical wavelength region and to be emitted, scattered or reflected by the object.
DE 32 33 013 A1 has disclosed an optical arrangement with the aid of which it is possible to detect and evaluate the spatial position of a 3-dimensional object by means of edge detection, and to determine the distance from the object. This arrangement can be applied chiefly in image evaluation systems for automatic manipulators. Two serially arranged lenses with different diaphragm openings, a raster filter and a television camera are used to detect the position of the three dimensions. Specific geometrical relationships are maintained both between these subassemblies inside the optical arrangement and in addition to the object to be imaged, in order to satisfy the imaging equations.
The raster filter comprises spatially distinctive, periodic structures such as, for example, sinusoidally cambered surfaces, lenses, cylindrical lenses or prisms with a prescribed bevel, or prism elements arranged in a crossed fashion. These structures make use of the refraction of the light beams, which are thereby deflected by a specific angle &agr; and thus displace the object points to be imaged. The brightness transitions at the edges of the object are periodically modulated by the periodic structures of the raster filter. They are picked up line by line by the television camera, and the signals are electronically evaluated. The periodic disturbances of the edge image contain in a form coded by the raster filter the information on the rotary position and the course of the object contours. The distance from the object is likewise derived, on the basis of the existing functional relationships, from the superimposition of the imaged object contours with the raster structure of the raster filter.
The use of refractive, spatial structures for the raster filter, as well as the use of two lenses and the maintenance of a series of geometrical conditions signify a comprehensive outlay on production and adjustment. Recording by the television camera is performed with the resolution prescribed by the video scanning.
CH 665 715 A5 has disclosed a method for measuring the angular displacement of an object by means of an object-referred aiming marker designed as an optically structured scanning disk. In this case, an image of the aiming marker is photoelectrically evaluated, and the information thus obtained is compared with a reference marker corresponding to the aiming marker. In detail, the aiming marker, which is provided with a defined center, is imaged onto the detection plane of a detector array, whereupon the values thus obtained are subjected to a correlation comparison with the reference marker. The displacement at the center of the aiming marker from the optical axis is then calculated from the result of the comparison. The available resolution of the structure and position of the object is given in this known method first and foremost by the individual detection ranges of the detector array, that is to say discrete pixel geometry, and correspondingly limited .
Under the title of “Theodolitsysteme fär industrielle und geodätische Messungen” [“Theodolite systems for industrial and geodetic measurements”], there is a description on pages 14 to 18 of the journal entitled Technische Rundschau No. 39, 1988 by W. Huep and O. Katowski of theodolite systems which are used for contactless measurement of surfaces such as, for example, claddings of aircraft or body parts with the aid of reflecting aiming markers. In this case, a search light arranged coaxially with the axis of the theodolite telescope illuminates an aiming marker which is imaged by the theodolite telescope on a CCD array as a spatially resolving detector. An electronic evaluation device with a computer determines the center point of the aiming marker image. The horizontal and vertical angle of the aiming marker are determined in a prescribed coordinate system from the coordinates of the center point of the aiming marker image on the CCD array.
Surface-reflecting spheres, for example chromized, polished steel spheres, which present the same aiming marker image in each case irrespective of the direction of observation serve as aiming markers. The reflecting spheres produce a virtual image, situated in the interior of the sphere, of the search light pupil of the theodolite, which is observed with the telescope of the theodolite and represented on the CCD array. Because of the short focal length of the spheres, however, the pupil image in the sphere is already small, as a result of limitation by diffraction, given a short distance between the theodolite and sphere, and it is smaller on the CCD array than the pixel size thereof. In order for it to be possible to take any picture at all, the theodolite telescope is defocused so as to produce a light spot which can be picked up by a plurality of pixels of the CCD array. The center point of the light spot thus obtained is determined by center or contour evaluation. However, because of the defocusing the different intensity distribution of the radiation in the light spot and its fuzzy edge leads to measuring errors.
In general, of course, it is possible to use lenses with a large image scale or an image scale which can be varied for range adjustment, in order to obtain a sufficiently large image on the CCD array. As a result, said defocusing of the theodolite telescope in order to produce a sufficiently large light spot diameter could be eliminated, for example. However, a large image scale entails the use of a correspondingly large lens focal length. Special telescope lenses or collimators have focal lengths of 2 m and more for this purpose. In this case, the range of angular measurement is necessarily substantially restricted for the same detector size. In addition, collimators with such focal lengths produce large-volume optical instruments of high weight.
It is the object of the invention to specify a method and a device by means of which it is possible, with a very low outlay on optical components and adjustments and in conjunction with drastically shortened mechanical overall lengths, to determine the direction of the optical radiation coming from an object within a large range of angular measurement, the aim being to achieve a precision which goes far beyond the spatial resolving power, conditioned by the design, of an optoelectronic detector to be used.
According to the invention, this object is achieved by virtue of the fact that an optical element is used to structure the wavefront of the radiation coming from the object in such a way that an intensity distribution with more than one intensity maximum is produced on the detector, and in that the direction to the object is determined from the measured intensity distribution by making use of the structure function of the optical element. Furthermore, the object is achieved by means of the features specified in the characterizing part of the device claim
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Advantageous developments and improvements of the invention follow from the features of the subclaims.
The radiation emitted by a point light source propagates spherically in all spatial directions in a homogeneous medium. This means that the surfaces of the same phase are spherical surfaces and expand. A spherical surface is virtually flat when seen at a large distance from its center point and in a small section. If the opening of an imaging optical system corresponds to this section, said opening receives an approximately plane wave or—seen in the beam image—
Braunecker Bernhard
Gaechter Bernhard F.
Rogers John Rice
Foley & Lardner
Le Que T.
Leica Geosystems AG
Luu Thanh X.
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