GEOMETRIC ERROR MEASUREMENT AND COMPENSATION IN TWO AXIS CNC MACHINE

Abstract

CNC machine tools are commonly used for manufacturing these days. CNC machines are meant for consistently producing parts, with high accuracy, with minimum scrape while maintaining high productivity. This big task can be achieved by precise and consistent positional control. Many factors affect the positional accuracy of CNC machines in which geometry of machine, temperature variations and force induced errors are major contributors. Geometric errors of the machine are result of manufacturing imperfections, assembly errors and wear and tear in the machine elements with the passage of time. To monitor the accuracy of the machines, machine measurement has become an important field of interest for research to ensure the quality assurance of manufacturing processes. Measuring machine errors in suitable manner and utilizing these machine measurements to enhance the accuracy and repeatability of the machines is the focus of this research. Geometrical errors of a two-axis CNC grinding machine has been measured and modeled to achieve better positional accuracy. Laser interferometer and geometrical artifacts are used for machine error measurement. Compensation for positional effect of these geometric errors was calculated based on the model and was compensated through NC program modification. Results were verified by taking measurements on a diagonal with laser interferometer which show a significant reduction in positional error. In addition to this work effect of software error compensation on accuracy of machined part has been studied on a milling machine. Positional errors of each axis were measured with Laser interferometer and compensated in the machine controller. Parts were machined before and after compensation and measured on CMM to analyze the effect. The CMM results show improvement in positional features of part machined after compensation.