Modeling and compensation of the interactions between geometrical errors and drive currents in directly driven gantry machine tools

Machine tools in gantry design are commonly used to produce very large workpieces e.g. in the aerospace industry. The increasing accuracy requirements of the workpieces demand a very stiff machine design. But high stiffness leads to increased force flux and tension within the machine tool due to existing geometric errors or thermal influences. Especially geometric errors in the rails impede the synchronous movement of the two gantry drive systems and lead to position errors. To achieve high positioning accuracy despite the named geometric errors, high drive forces are necessary. These drive forces tension the gantry bridge. However, high forces lead to increased drive currents and, thus, reduce the machine dynamics and increase the energy consumption. In this paper, the interactions between geometrical errors and drive currents are investigated. Based on that, a multi-variable control to compensate for these tensions is introduced. That way the tension currents have been reduced by 86 %.