Leica Geosystems Ag

Raimund Loser

Albert Markendorf

Jürgen Dold

Bernhard Hauri

Roland Zumbrunn

A measurement system for determining six degrees of freedom (&#x3b1;, &#x3b2;, d, &#x3c6;, &#x3c7;, &#x3c8;) of a reflector () or of an object () on which the reflector is arranged, comprises an angle- and distance measurement apparatus (), e.g. a laser tracker, operating with a laser beam as a measurement beam (). The reflector () is designed for a parallel reflection of the measurement beam () and has an apical opening or surface (), in a manner such that a part of the measurement beam () directed onto the reflector (), passes through the apical opening or surface (), and is incident on a light-sensitive surface () arranged behind the reflector apex. Five degrees of freedom (&#x3b1;, &#x3b2;, d, &#x3c6;, &#x3c7;) of the reflector () or the object () are computed from measurement data produced by the angle- and distance measurement apparatus () and by the light-sensitive surface ().

Measurement system for determining six degrees of freedom of an object

For indirect determination of point positions and/or of surface orientations in point positions a laser tracker ( ) adapted for relative and absolute distance measurement is used. A measuring device is utilised, the device including a target point (retro-reflector ) for the laser beam of the tracker, the target point being movable along a trajectory path (A). The position and orientation of the trajectory path (A) of the target point is precisely defined relative to a reference point (R) of the device ( ) and the device ( ) is positionable in the region of a point position (P) to be determined such that the position of the reference point (R) relative to the point position (P) to be determined is precisely defined. For determining the point position (P), the device ( ) is positioned in the region of the point position (P) to be determined, the target point is positioned in a starting position ( ) and is detected by the tracker ( ) by direction determination and absolute distance measurement. Then the target point is moved along the trajectory path (A) being followed by the tracker ( ), while direction and distance changes are recorded. In comparison with an indirect determination of a point position with the help of a known measuring tool having a plurality of stationary target points for the tracker beam, the determination by means of the target point moving along the trajectory track (A) is more simple and more accurate.

Indirect position determination with the aid of a tracker

Using a laser-tracker ( ) with an interferometer together with a retroreflector ( ) in the form of a triple prism or a triple mirror arranged on an object and designed for parallel reflection of the laser beam ( ) directed to the reflector ( ), the position of the object is computed by way of measurement data with respect to the direction of the laser beam ( ) and its path length. Additionally the spacial orientation of the object ( ) is determined by producing additional measurement data with respect to the angle of incidence (&agr;) of the laser beam into the reflector ( ) and/or with respect to an adjustable orientation of the reflector ( ) relative to the object ( ) and by computing the position and spacial orientation of the object ( ) by way of measurement data with respect to the direction and the path length of the laser beam ( ) and by way of this additional measurement data. Thereby the measurement data of the direction measurement and of the interferometric measurement may be corrected by way of the additional measurement data with respect to the angle of incidence (&agr;) such eliminating their dependency on the angle of incidence. For determining the angle of incidence (&agr;), the reflector ( ) is designed in a manner such that a central part of the laser beam ( ) passes through the reflector ( ) unreflected and behind the reflector ( ) impinges a position sensor ( ) arranged stationarily relative to the reflector, while a peripheral part of the laser beam ( ) is reflected parallel and used for the interferometric measurement.

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Bad Säckingen, Germany

Raimund Loser