Application Notes AP 1121

How to measure the 18 positioning errors and Circular contouring errors with a single laser system MCV-500C

II. What is MCV-500C? The MCV-500C Complete Laser Calibration System is designed for the measurement of both the static positioning errors (18 errors of the 21 rigid body errors) and dynamic contouring errors. The MCV-500C can perform a quick check of the machine's performance based on the ASME B5.54 standard's one-day test. Using the laser vector technique, the volumetric positioning errors, including 3 displacement errors, 6 straightness errors and 3 squareness errors can all be measured. The measured errors can be used to generate a volumetric compensation file to achieve higher volumetric positioning accuracy. The volumetric error compensation sometimes called straightness error compensation (Fanuc), sag compensation (Siemens), non-linear compensation (Heidenhain), cross compensation (Fidia), or 3-D compensation (Fanuc 15I). We have demonstrated that using the volumetric error compensation, the volumetric positioning accuracy can be improved by a factor of 3 to 10. I. What is the problem Most system tool operators know that for a 3-axis machine, just calibrating the 3 displacement errors or just compensating 3-axis pitch errors is not enough. There are 21 positioning errors, namely, 3 displacement errors, 6 straightness errors, 3 squareness errors, 3 pitch angular errors, 3 yaw angular errors and 3 roll angular errors. All of the 21 positioning errors may contribute to the volumetric positioning accuracy. Most laser interferometers can measure all of the above errors, except the 3 roll angular errors.Hence a total of 18 positioning errors can be measured. However, using a conventional laser interferometer, the measurement of straightness errors and squareness errors requires very complex and expensive optics. It is extremely difficult to setup and align and also very time consuming. Conventional method for the circular contouring error measurement is using a telescoping ballbar or double ballbar. It is separate equipment. The measurement is contact with limited performance. The ASME B5.54 and ISO 230 standards recommended 4 body diagonal displacement error measurement and circular contouring measurement to ensure the machine performance. However, if the machine is out of tolerance, the source of errors cannot be determined by the body diagonal displacement measurement and the circular contouring measurement.
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