Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1995-03-03
1997-01-28
Pham, Hoa Q.
Optics: measuring and testing
By polarized light examination
With light attenuation
356373, 33707, G01B 1100
Patent
active
055982689
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1) Field of the Invention The invention relates to a process for determining the location of a positioning body in relation to a reference body 1 and a device for implementing the process.
2) Discussion of Related Art Such a process serves, e.g. to measure the distance between longitudinally moveable objects, like automatic measuring heads, gripping arms or assembly arms, during the control sequence of measuring and production machines. In so doing, the accuracy with which these distances can be determined is a decisive factor for the production accuracy of the automatic machines.
A process that enables high accuracy of measurement independently of an exact guide for the scanner is already known from the DE-OS 39 09 856. Here, three marks of a scale are evaluated by a scanner. With two marks, an angle of projection formed between a center of projection and these marks would still depend on the distance that the center of projection is above the marks and how far it is offset laterally. With three marks, however the center of projection can be determined exactly via the other angle of projection between the center of projection, the other mark and one of the other marks. For a combination of two combined angles there exists only one single place, at which the center of projection can be located.
In addition, it is known from the DE-PS 41 04 602 U.S. Pat. No. 5,401,226) to calculate the coordinates of the center of projection of an imaging lens from the known coordinates of marks on the scale via the projecting relationship between the projection surface of the scanner and the plane of the scale. The marks obtain their coordinate information with respect to the scale in coded form. The coordinate information is decoded during the calculation.
Furthermore, it is known from the book by G. Konecny and G. Lehmann: Photogrammetry, 4th edition, de Gruyter, Berlin--New York, 1984, pp. 48-55, to utilize a projecting relationship in order to determine the coordinates and to take into consideration an angle of tilt between a projection surface and the plane of the original image. To produce the projectivity between two planes, four known points are used.
SUMMARY OF THE INVENTION
The invention is based on the problem of determining all of the parameters of the location of a positioning body with respect to a reference body with one single scanner.
In the invention the marks contain the absolute information of their coordinates on the scale in coded form. The coding is put into practice as different line thicknesses. The centers of the intersection regions of the marks correspond exactly to the locations described by the coding.
A relation between the coordinates on the positioning body, thus the plane of the scale bearing the marks and the projection surface of the scanner, exits via the projecting relationship. The relation can be described by means of equations of the collinear transformation, whose general formula reads: ##EQU1## They are two equations with 8 unknowns. If four centers are selected, eight equations can be set up and the eight unknowns can be determined by this method. In this manner, it is possible to state all of the parameters for determining the spatial location of a positioning body relative to a reference body (six degrees of freedom).
The exact calculation can be done with the formulas, appearing below which are already resolved for the coordinates of the center of projection and the angle of orientation between the projection surface of the scanner and the plane of the scale.
An improvement provides that more than four centers are determined by the intersection regions of the marks on the surface scales and that a balancing calculation be done.
For more than four centers there is agreement. If these other centers are used in the calculation, the results of the measurement can be improved by the balancing calculation. In this manner the inaccuracies in the mechanical design of the marks and the scanner, optical errors and rounding off errors can be reduced in the
REFERENCES:
patent: 5017013 (1991-05-01), Kellner
patent: 5317388 (1994-05-01), Surka et al.
patent: 5404226 (1995-04-01), Kellner
patent: 5456020 (1995-10-01), Kellner
"Photogrammetrie", Gottfried Konecny and Gerhard Lehmann, 4th edition, de Gruyter, Berlin-New York, 1984, pp. 48-55.
E.M.S. Technik GmbH
Pham Hoa Q.
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