Five-axis machine tools have significantly contributed to the industrial development, and the continuous technological advancement have seen an increase in the demand for highly accurate and reliable five-axis machine tools. Local errors including thermal errors and geometric errors and position of the axes have been identified as major factors influencing the machine tool accuracy. The accuracy has been improved through modeling and compensation of the geometric errors by eliminating or greatly reducing the integrated volumetric errors to realize tool poses close to the design poses. Software compensation is preferred over hardware compensation since its more economical and easier to implement. However, they are unsuitable for design and manufacturing of machine tools. Thus, better strategies for effective implementation of hardware compensation are highly desirable.
Recently, sensitivity analysis has been used to identify the influences of system parameters on system responses. However, error sensitivity analysis does not take into account the values of error components that change with the motion of the corresponding axis making it difficult to design error components for error compensation. Therefore, it is very important to determine the key axes that greatly affect the machine tool accuracy for effective implementation in hardware compensation.
To this note, Dr. Guoqiang Fu, Hongwei Gong (graduate student) and Professor Hongli Gao from Southwest Jiatong University in collaboration with Professor Jianzhong Fu from Zhejiang University and Dr. Xiaolei Deng from Quzhou University investigated the geometric error contribution of all axes to the accuracy of machine tools by establishing the sensitivity matrix of each axis. First, a product of exponential theory was used to determine the error vector components of the position-independent errors. Secondly, the formula was utilized to establish the error contributions of all the axes by transforming the differential changes between the coordinate frames. Finally, two methods: one using the error sensitivity coefficients and the other employing the weights of the error contributions of the axes were employed to determine the crucial axis affecting the accuracy of the five-axis machine tools. The work is published in the International Journal of Machine Tools and Manufacture.
Results showed that it was possible to establish precise error vectors of each axis. The summation of the error contributions of all the axes was regarded as the integrated geometric error of the machine tool. Additionally, the two error sensitivity evaluation methods were used to determine the critical axes, which were thereafter used to analyze the geometric error compensation. As proof of the concept, the effectiveness of the error contribution modeling and error sensitivity evaluation of the axis was validated based on the simulations of the real cutting experiments on the smartCNC500-DRTD five-axis machine tool. Specifically, a simulation based on the hardware compensation, where the local errors of the crucial axes were set to zero, was proposed. The error sensitivity evaluation proved effective.
In a nutshell, a combined advantage of the product of exponential theory and transforming differential changes between the coordinate frames greatly contributed to the calculation of the geometric error contribution and error sensitivity analysis of the machine tool. According to Dr. Guoqiang Fu, the study insights will pave the way for low-cost error compensation for efficient design and manufacture of accurate machine tools.
Reference
Fu, G., Gong, H., Fu, J., Gao, H., & Deng, X. (2019). Geometric error contribution modeling and sensitivity evaluating for each axis of five-axis machine tools based on POE theory and transforming differential changes between coordinate frames. International Journal of Machine Tools and Manufacture, 147, 103455.
Go To International Journal of Machine Tools and Manufacture
