Method for correcting measurement errors in a machine measuring co-ordinates

A method for determining a correction function {overscore (K)}({overscore (r)}jk) for rectifying the coordinate-dependent measuring errors of a coordinate-measuring machine by selfcalibration, comprising, in a stepwise fashion:

• a) measuring initial coordinates {overscore (r)}j0 in relation to a number j of reference structures (5) on a rigid, uncalibrated reference object (1) disposed on an object table of the coordinate-measuring machine in an initial orientation k=0 of the reference object (1), and measuring calibration coordinates {overscore (r)}jk in a number k≧1 of different calibration orientations produced by rotation from the initial orientation, wherein the calibration orientations are produced by rotations with the aid of rotation functions Dk about a single rotation axis (6) of the reference object (1),
• b) operating a coordinate dependent correction function {overscore (K)}({overscore (r)}jk) upon the initial coordinates {overscore (r)}j0 and the calibration coordinates {overscore (r)}jk, the coordinate-dependent correction function {overscore (K)}(jk) is described by an approximation K _ ⁡ ( r _ jk ) ≈ ∑ i = 0 N ⁢ a i * k _ i ⁡ ( r _ jk )
• with initially unknown fit parameters ai and a number N of prescribed, linearly independent fit functions {overscore (k)}i({overscore (r)}jk);
• c) performing rotation functions Dk upon the corrected calibration coordinates ({overscore (r)}jk+{overscore (K)}({overscore (r)}jk));
• given by the calibration coordinates {overscore (r)}jk operated upon by the correction function {overscore (K)}({overscore (r)}jk) to rotate back the calibration coordinates into the initial orientation;
• d) calculating fit parameters ai such that in relation to a reference structure (5) in each case all the corrected and rotated-back calibration coordinates Dk({overscore (r)}jk+{overscore (K)}({overscore (r)}jk)) and the corrected initial coordinates ({overscore (r)}j0+{overscore (K)}({overscore (r)}j0)) substantially agree, and
• e) generating a continuous correction function {overscore (K)}({overscore (r)}jk) to be applied to arbitrary coordinates to be measured wherein, from the fit functions {overscore (k)}i({overscore (r)}jk), no linear combinations can be formed which go over into themselves for all the rotations Dk carried out.