Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1996-12-16
1998-05-26
Font, Frank G.
Optics: measuring and testing
By polarized light examination
With light attenuation
3561413, 3561411, 3561521, G01B 1126
Patent
active
057574995
DESCRIPTION:
BRIEF SUMMARY
The present invention relates in general to a method of locating the spatial position of a frame of reference, i.e. a method making it possible not only to find the position of the origin of the frame of reference relative to a fixed frame of reference, but also to find the orientations of its three axes. The invention also relates to apparatus for implementing the method.
BACKGROUND OF THE INVENTION
In the particular field of techniques for measuring the shape and/or the position of an object by means of a three-dimensional measuring machine, there is an ever-increasing demand for machines that are simultaneously compact, lightweight, and accurate. By way of example, this problem is becoming particularly acute for measuring the positions of objects inside the bodywork of a motor vehicle.
Machines designed twenty or so years ago were bulky and expensive (see for example documents U.S. Pat. No. 3,774,312, U.S. Pat. No. 3,744,311, U.S. Pat. No. 3,636,635, U.S. Pat. No. 3,279,079). Also, those machines were of limited application since the size of the machine determines the size of the objects that can be measured, and the cost of the machine increases rapidly with size. Because of difficulties in maintaining positioning accuracy and in displacing cantilevered-out elements, machines of that type must also be entirely solid in order to have sufficient rigidity, so that measuring objects of large dimensions (in length or in height) makes it necessary to use machines that are bulky, heavy, and expensive.
Machines that are simpler and handier have been proposed, as illustrated by documents U.S. Pat. No. 3,944,798 and GB-A-1 498 009, or more recently in document FR-A-2 597 969. Those machines are generally constituted by a support and a deformable arm made up of hinged arm segments, in association with a contact sensor mounted at the end of the last arm segment. The assembly formed in that way is connected to a computer which uses information delivered by the sensor and by position detectors associated with the hinged arm segments. Nevertheless, those machines are more restricted as to accessible length and measurable volume, which turn out generally to be restricted to about one meter from the support of the deformable arm. As a result, if it is desired to perform measurements in a zone that is further away, it is necessary to displace the support. That gives rise to the problem of determining the spatial location of the support since in order to associate a series of measurements performed in a given position of the support with a fixed frame of reference, it is necessary to know the position and the orientation of the support relative to said fixed frame of reference.
Position locating techniques using triangulation are also known.
For example, document EP-A-0 143 012 describes a three-dimensional measuring machine that includes a fixed stand and a measurement head that is movable in a horizontal plane. The measurement head comprises firstly a distance sensor using a vertical laser beam illuminating the point concerned to measure its distance from the measurement head, and secondly means for locating the position of the head in the horizontal plane. Said position-locating means comprise a laser source pivotally mounted about a vertical axis on the measurement head to illuminate in succession three fixed targets disposed in the plane so as to deliver a signal indicating when they are being illuminated by the beam from the laser source. The angular position of the laser source about its vertical axis of rotation is measured by an associated position sensor which, when the targets are illuminated, finds the corresponding angular positions of the source. On the basis of the above information and information relating to the positions of the targets, an electronic processor unit computes the position of the measurement head in the horizontal plane. Nevertheless, that installation is strictly limited to use in two dimensions.
Similarly, documents GB-A-1 181 162 and U.S. Pat. No. 5,258,822 describe devices for provi
REFERENCES:
patent: 4651283 (1987-03-01), Sciaky et al.
patent: 4732471 (1988-03-01), Cain et al.
patent: 5187540 (1993-02-01), Morrison
patent: 5198877 (1993-03-01), Schulz
Ferguson Jr. Gerald J.
Font Frank G.
Robinson Eric J.
Smith Zandra V.
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