A new conceptual approach for systematic error correction in CNC machine tools minimizing worst case prediction error

Abstract

A new artifact-based method to identify the systematic errors in multi-axis CNC machine tools minimizing the worst case prediction error is presented. The closed loop volumetric error is identified by simultaneously moving the axes of the machine tool. The physical artifact is manufactured on the machine tool and later measured on a coordinate measuring machine. The artifact consists of a set of holes in the machine tool workspace at locations that minimize the worst case prediction error for a given bounded measurement error. The number of holes to be drilled depends on the degree of the polynomials used to model the systematic error and the number of axes of the machine tool. The prediction error is also function of the number and location of the holes. The feasibility of the method is first investigated for a two-axis machine to find the best experimental setting. Finally based on the two-axis case study, we extend the results to machine tools with any number of axes. The obtained results are very promising and require only a short time to produce the artifact

Assessing the uncertainty of the means for determining the positioning accuracy of the machine

“…Standard deviations, defined by machines positional accuracy are important parameter affecting the: -accuracy of compensation of characteristic systematic errors, connected to machines geometrical accuracy [3];…”

Integrated geometric and thermal error modeling and compensation for vertical machining centers

“…To improve the approximation performance of the prediction model within the entire working space and to reduce the uncertainty of the parameter estimates in the modeling process [11], the Chebyshev nodes are used here to choose the optimal measuring points for the error components.…”

“…(14)) was frequently used for geometric error approximation [11]. In theory, as the order of polynomial increases, the approximation accuracy is expected to increase.…”

“…Zhu et al [10] proposed a statistical method for the extraction of machine tool geometric error components, and then a volumetric error mapping was constructed for numerical compensation. Chung et al [11] introduced a new conceptual approach to identify the closed loop volumetric errors of multi-axis machine tools based on a manufactured artifact.…”

Procedure for geometrical errors identification in machine tool

“…Moreover, the results provided by these procedures are influenced by a combination of kinematic, dynamic and thermal effects. Nevertheless, it does exist a real effort in identifying the geometrical errors of a MT by machining some specific workpieces as can be seen in Ibaraki et al (2010) or in Chung et al (2012). On the other hand, most of the research related with the development of verification procedures has been traditionally restricted to the identification of the geometrical (kinematic) errors of MT (under no-load or quasi-static conditions) because they are supposed to be the main contributors to total error, as can be seen in Sartori and Zhang (1995) or Schwenke et al (2008), even in international standards as ISO 230.…”