Property model-based correction of load-dependent structural deformations

 

In addition to the static and dynamic behavior, the machining accuracy of machine tools is essentially determined by thermal influences. Various internal and external heat sources lead to an unsteady temperature distribution within the machine structure and thus to displacements of the tool center point. While the current state of the art allows relatively good correction of spindle-related growth in the z-direction, this applies only to a limited extent to the remaining misalignment components.

The German Research Foundation - DFG - is funding this project with the aim of minimizing volumetric thermo-elastic displacements of machine tools. A volumetric measurement methodology based on tracking interferometers has already been qualified for the detection of thermally induced volumetric errors. This measurement methodology forms the basis for the subsequent development of a correction model which corrects the occurring displacements on the basis of internal control data without the integration of additional measurement technology such as temperature sensors.

Specially designed and manufactured hydraulic load units for spindle and linear axes enable the targeted investigation of the load-dependent thermo-elastic machine behaviour. Previous tests have shown that thermo-elastic structural deformations due to axle loads are highly pose dependent. In this case, a position-independent correction cannot provide a satisfactory result. The considered error parameters according to ISO 230 are influenced to varying degrees by a thermal axle load, so that the development of a correction algorithm can be focused on individual error parameters. In the further course of the project, the focus is on thermo-elastic displacements due to ambient temperature fluctuations and loads on rotary axes.