Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1986-09-30
1989-06-20
Tarcza, Thomas H.
Optics: measuring and testing
By polarized light examination
With light attenuation
356154, 356138, G01B 1126
Patent
active
048404900
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method and apparatus for measuring the position in a plane of an intersectable beam passing through the plane or the position of a tangible object located in a plane. The invention finds particular application to measuring the position of a laser beam relative to a structure to be monitored and will be described in relation to the detection of the position of a beam.
BACKGROUND TO THE INVENTION
It has been proposed to use a laser beam as a spacial reference against which the movement of a portion of a natural or man-made structure can be measured. The laser can be mounted at a reference point to be directed adjacent a structure to be monitored. The portion of the structure monitored carries a target which intercepts the beam to measure the position of the beam relative to the target. In one prior proposal the target normally allows the beam to pass whereby a number of such targets can be mounted at different points of the structure spaced along the beam. One such target employs two orthogonal straight edges individually movable to intercept the beam so that by measuring the positions of the straight edges at the points of interception the beam position is measured in Cartesian coordinates. For a further discussion of this kind of detection system reference may be had to published International Application No. WO85/00222 which was published on Jan. 17th, 1985, that is after the priority date of the present application, and which corresponds to commonly assigned U.S. application Ser. No. 705,469 filed Feb. 21, 1985.
Various other techniques for using laser beams in position measurement have been disclosed in British patent specification Nos. GB 1550934, GB 1511265, GB 1483021, GB 2074808 and GB 2090096A. The present invention is concerned with the detection of a beam by intersection of two target edges with the beam but adopts a different approach to that set out in the abovementioned application WO85/00222.
SUMMARY OF THE INVENTION
According to one aspect of the invention there is provided a method of detecting the position of a laser beam or other object in which two curves are moved along respective predetermined paths for the beam to impinge thereon, the curves having a shape such that the sum of their displacements from reference positions to be impinged on by the beam is a monotonic function of the distance of the beam or other object from an axis from which such distance is determined as one coordinate of beam position and that at least one displacement from a reference position is used to determine a position for the beam or other object as a second coordinate of beam or other object position.
The two curves may be in fixed spaced apart relation having a common reference position. For example they may be formed as spaced edges of a target structure that is either linearly movable in the direction of an axis or rotationally movable about an axis. The linear or angular spacing, as the case may be, is a monotonic function of distance from the axis in question. A theoretical derivation of suitable curves, which in the linear case may be straight lines, is given hereinafter for both cases. Ideally to minimise error in position of a laser beam or other object is 90.degree.. The angle is defined as the angle between the respective tangents to the curves at the point they intersect. In the case of the rotary target structure it will be shown how a curve based on a simple arc can be oriented to achieve a sufficiently close approximation while achieving the 90.degree. intersection angle at at least one radial value.
In the case of fixed curves, the edges preferably define therebetween a detection notch as it is called hereinafter within which the beam or other object lies. Preferably the target structure is symmetrical and the common reference axis is the axis of symmetry. The sum displacement, linear or angular, is the spacing between the two edges at the points at which they intersect a given beam or other object position. If this position is offset f
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Audus David
Gabriel David
Strange Norman
Hellner Mark
Lasercheck Limited
Tarcza Thomas H.
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