Self-Calibration Method for Three Dimensional Coordinate Measuring Machines Using a Ball Plate

The proposed self-calibration method, like other methods, uses a ball plate for the error identification, but unlike other methods the ball plate needs not to be calibrated, i.e. the distances between the different balls on the plate need not to be known accurately. After the measurement of the ball plate in different positions in the measuring volume, the systematic geometrical errors in the geometric error model of the measuring machine can be computed. This geometrical error model is used by the software error correction to correct on-line every single measurement of the measuring machine. This results in a higher accuracy for the measuring machine. The self-calibration method has been carried out on a CNC 3D-CMM and the resulting software error correction has been evaluated using stepgauge measurements. The evaluation results show that the systematic geometrical errors are largely reduced.