Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1998-04-10
1999-10-26
Rosenberger, Richard A.
Optics: measuring and testing
By polarized light examination
With light attenuation
G01B 1103
Patent
active
059737883
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present application relates to a system for point-by-point measuring of spatial coordinates.
BACKGROUND
Industrial geometric measuring is carried out today using a number of different methods. The most used optical methods are: conventionally are based on photographic film, or more recently, are based on electronic sensors; light and the detection of the phase of the returned beam, or on laser interferometry.
Modern photogrammetry systems, also known as videogrammetry systems, are based on video camera techniques. These register the position of points in the form of active light sources, reflecting points or characteristics of the object to be measured (e.g., holes). The points may be registered simultaneously by two or more cameras, or they can be imaged sequentially from a number of different camera positions. The spatial position of the points is calculated using mathematical methods which include the automatic determination of the position and orientation of the cameras for each individual image, and also correction for the cameras' lens errors and other factors which produce a non-ideal image. The cameras may also be pre-calibrated, i.e., correction of the image points is based on a calibration table or other mathematical correction.
Modern photogrammetry systems are marketed by the Norwegian company Metronor AS, the Swiss company Imetric SA and the US company GSI (Geodetic Services Inc.) Metronor's system is described in Norwegian Patents Nos. 164 946, 165 046, 169 799, 174 025, and also Norwegian Patent Application No. 931873.
Metronor's system is based on pre-calibrated cameras. The system is optimized in order to determine the position of active light sources. A measuring tool known as a light pen is used to mark the points that are to be measured. The light pen has a minimum of three light sources in known positions relative to its contact point. The coordinates of the contact point can be determined by simultaneously taking the image of the light sources.
Imetric and GSI offer systems where the cameras are not pre-calibrated, but are calibrated for each individual measuring operation. The cameras register the position of retroreflector targets. These are illuminated by flash lamps mounted on the cameras. The companies have also developed touch tools similar to Metronor's light pen, where the active light sources are replaced by retroreflector targets.
The photogrammetry systems determine directions in space through imaging (projection). The accuracy depends on the quality of the camera, the nature of the points to be measured, and in particular on the geometrical factors. Geometrical factors which influence accuracy are position, density and distribution of measuring points, the number of cameras or images, and position and orientation of the cameras, and also whether the cameras' lens errors are pre-determined.
The chief disadvantage of photogrammetry systems is that a measuring point must be registrable by two cameras simultaneously or in sequence by locating a camera in at least two different positions.
Laser rangefinders based on interferometry are internationally known under the product name "Laser tracker". A laser tracker consists of a laser, a mirror system for controlling the laser, a reflector unit, distance and direction sensors, and a computer. The reflector unit, also known as a "corner cube" or prism reflector, reflects light back parallel to the emitted beam. The laser beam is steered so that it always strikes the reflector unit. This is accomplished in that the laser tracker contains a sensor which detects the striking point on the reflector unit. In general, a laser tracker registers both direction and distance, and hence three-dimensional coordinates of the measuring point. The distance is determined by interferometry. The direction is determined by registering the orientation of the mirrors. The distance measurement exhibits high accuracy, whereas the direction is often determined with less precision.
Laser trackers have major disadvantages: refl
REFERENCES:
patent: 5305091 (1994-04-01), Gelbart et al.
patent: 5440392 (1995-08-01), Pettersen et al.
patent: 5729475 (1998-03-01), Romanik
Pettersen Alf D.
R.o slashed.tvold .O slashed.yvind
Metronor ASA
Rosenberger Richard A.
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