Measurement and evaluation of the volumetric accuracy of multi-axis machine tools under operational conditions

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The working accuracy of a machine tool directly influences the quality of the manufactured products. An essential criterion for evaluating the operational capability of a machine tool is its ability to assume the specified positions of the tool centre point (TCP) and the spatial orientation of the tool as accurately as possible during machining. This spatial movement accuracy is limited by geometric and kinematic deviations. These include, for example, the manufacturing accuracy of the mechanical assemblies, static, dynamic and thermal influences as well as influences from friction or lubrication and from the setting variables of the machining process. The aim of the research project is to develop a new method for determining and correcting the spatial movement accuracy of a machine tool based on the double ball bar (DBB) measurement principle. The method must be suitable for self-testing, i.e. it should be possible to carry out and automate it quickly and without costly conversions on machines that are ready for operation during breaks in machining. Moreover, it should not require personnel specially qualified for these measuring tasks. The measuring equipment to be used must be sufficiently accurate for the measuring task, easy to handle, robust for use in a machining environment and inexpensive. In the first phase, a DBB measuring system with an extended measuring range was developed, the prerequisites for the synchronised acquisition of the data of the measuring system and the actual axis values of the test machines were created and the fundamentals of the generation of error-sensitive spatial measuring paths were worked out. The aim of the second phase is to increase the spatial path accuracy by identifying and correcting kinematic errors from the measurement data.