3D Volumetric Positioning Measurement and Compensation of CNC Machines Using Laser Vector Technique

The worldwide competition and quality standards such as ISO 9000 and QS 9000, demanded tighter tolerance and regular maintenance of all machine tools. Twenty years ago, the largest machine tool positioning errors are lead screw pitch error and thermal expansion error. Now, most of the above errors have been reduced by linear encoder and compensation. The largest machine tool positioning errors become squareness errors and straightness errors. Hence, to achieve higher 3D volumetric positioning accuracy, all 3 displacement errors, 6 straightness errors and 3 squareness errors have to be measured and compensated. Using a conventional laser interferometer to measure these errors is rather difficult and costly. It usually takes days of machine down time and experienced operator to perform these measurements. Optodyne has developed a new laser vector measurement technique for the measurement of these errors in a few hours instead of a few days. The measured errors can be used to generate 3D volumetric compensation files to compensate the volumetric positioning errors and achieve higher volumetric positioning accuracy. To determine the angular errors, 3 displacement measurements along the same axis but at different Abbe offsets can be used. Hence all 18 errors can be determined. Reported here are the basic theory and operation, the hardware, the data collection and analysis, and the test results. Using the laser vector technique the volumetric positioning errors of 4 Deckel Maho Gildemeister 3-axis milling machines with Heidenhain controller have been measured. For each axis, the linear displacement errors were also measured at 3 different locations. Data were collected with 5 bidirectional runs over 4 machines. The averaged linear displacement errors at the center of working volume, the pitch and yaw angular errors, and their statistical deviations can all be calculated. The agreement between all different measurements was within the statistical deviation.