Thermally induced volumetric error compensation by means of integral deformation sensors

Abstract

A common approach to describe errors in machine tools is the volumetric error modeling. For three-axis machine tools, this includes a structural loop model of 21 geometric/kinematic error components. The dislocation at the tool tip is then the result of the kinematic decomposition of these error components and can be derived with simple mathematical techniques. The concept behind this modeling approach is that geometric/kinematic errors include a time-invariant, deterministic term and a time-variant, load-dependent, stochastic term. Thermal effects cause the most detrimental time-variant term. In order to include them in volumetric error models, the variation of the error components with respect to the thermal loading on the machine tool structure has to be measured. The most of the research has focused until now on measuring the variation of the most significant error components with temperature. Collecting these data is however difficult and time-consuming and the resulting models are too cumbersome for the industrial use. This paper proposes a new method for calculating thermally induced volumetric error based on the direct measurement of the structural deformations. This measurement has a higher content of information than common temperature sensor methods, since the structural deformations are the outcome of all thermal sources combined. To demonstrate the effectiveness of the proposed model, several thermal loads were applied on a three-axis milling machine, while the dislocation at the tool tip was measured with an R-test based procedure.