Abstract
Gantry-type computer numerical control (CNC) machines are widely used in the manufacturing industry. A novel structure with moveable gantry is proposed to improve the traditional gantry-type machine structure’s disadvantage of taking up too much space. Geometric errors have direct impacts on the actual position of the tool, which significantly reduces the accuracy of machines. Errors of different components are always coupled and have uncertain effects on the total geometric error. Thus, it is essential to find an effective way to identify the dominant errors and do targeted compensation. First, a novel identification method using value leaded global sensitivity analysis (VLGSA) is proposed to find the dominant errors. In VLGSA, weighting factors which show the influence of the error range are used to modify the multi-body system (MBS) error model. Results show that the dominant errors in three directions respectively contribute 80%, 86% and 85% of the total error in their directions. Then, errors identified by VLGSA are modeled by least-square linear fitting and B-spline interpolation methods, respectively, according to the feature of error data. Finally, the models are applied in a new real-time compensation system developed on the Beckhoff TwinCAT servo system. Experimental results from the gantry-type CNC engraving and milling machine show the proposed method can help figure out the most dominant errors and reduce around 90% of the total error.
Highlights
Gantry-type manufacturing equipment has already played an indispensable role in the modern manufacturing industry
After compensation aiming at dominant error components components calculated by the value leaded global sensitivity analysis (VLGSA) method, the total error of the X direction in space movement calculated by the VLGSA method, the total error of the X direction in space movement reduces around reduces around 90%
Structural and motional geometric errors widely exist in computer numerical control (CNC) machines
Summary
Gantry-type manufacturing equipment has already played an indispensable role in the modern manufacturing industry. J.X. et al [5] took further research based on the fundamental principle of Paul and Veitschegger, by analyzing the differential movement and differential transformation They proposed a comprehensive method of both discovering how geometric error propagates through every single axis. [10] built the error model of the classic three-axis machine tool, decomposed the final error into the errors existing in the components in the whole motion chain These works showed the development and application of different error modeling methods, gave inspirations to further research. Using cubic spline interpolation established the thermal and geometric error model and improved the position accuracy of the CNC machine. Value leaded global sensitivity analysis (VLGSA) is proposed and used in the above analysis process, in which the measurement value of each error item is considered to modify the total geometric error model. The compensation experiment verified the validity of the above crucial error finding and compensation method
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