Five-Axis Machine Tool Volumetric and Geometric Error Reduction by Indirect Geometric Calibration and Lookup Tables

Abstract

Modern CNC machine tools provide lookup tables to enhance the machine tool's precision but the generation of table entries can be a demanding task. In this paper, the coefficients of the 25 cubic polynomial functions used to generate the LUTs entries for a five-axis machine tool are obtained by solving a linear system incorporating a Vandermonde expansion of the nominal control jacobian. The necessary volumetric errors within the working volume are predicted from machine's geometric errors estimated by the indirect error identification method based on the on-machine touch probing measurement of a reconfigurable uncalibrated master ball artefact (RUMBA). The proposed scheme is applied to a small Mitsubishi M730 CNC machine. Two different error models are used for modeling the erroneous machine tool, one estimating mainly inter-axis errors and the other including numerous intra-axis errors. The table-based compensation is validated through additional on-machine measurements. Experimental tests demonstrate a significant reduction in volumetric errors and in the effective machine error parameters. The LUTs reduce most of the dominant machine error parameters. It is concluded that although being effective in correcting some geometric errors, the generated LUTs cannot compensate some axis misalignments such as EB(OX)A and EB(OX)Z. The Root Mean Square of the translational volumetric errors are improved from 87.3, 75.4 and 71.5 µm down to 24.8, 18.8 and 22.1 µm in the X, Y and Z directions, respectively.

Laser Tracker-Based on-the-Fly Machine Tool Calibration without Real-Time Synchronization

“…With the developed OTF method as the input data, there must be enough information to (ideally) unambiguously discern geometric errors. Due to the concept of not taking information on path direction into account, there is no full volumetric error information available at each point on the path, as is with some other indirect calibration methods [1,6,7,12,18]. Hence, path-planning algorithms as calibration preparations must consider said fact and ensure discernability.…”

Modeling, detection, and validation for geometric errors in machine tools

“…Ibaraki et al [5], through experimental machining, detected geometric errors in the rotational axis of the machine tool and validated the error identification by using a touch-triggered probe. Esmaeili et al [6] identified machine tool geometric errors through on-machine measurements, subsequently validating the error compensation with additional machine measurements.…”

A data-driven high-precision modeling method of machine tool spatial error under the influence of Abbe error

“…There are many ways to measure geometric errors of CNC systems. According to the different measurement theory, these methods can be divided into indirect measurement [8,9] and direct measurement [10] . For the indirect measurement method, it is mainly to carry out three-coordinate detection of processed products or use special measuring blocks to indirectly obtain geometric errors of machine tools.…”

“…And for the direct measurement method,in order to realize the measurement of the single error of the machine tool, the optical instrument is mainly used to identify the changes in the reflected optical path of the optical mirror group as the machine tool moves. Such methods include laser tracker measurements [12,13] , laser interferometers [14][15][16] and 1D spherical error array measurements [17] . The laser interferometer measurement method is widely used due to the advantages of measurement efficiency and it has become the main research direction on error compensation.…”