Untersuchung eines magnetischen Lagerungskonzepts einer rotierenden Schleifkugel für achsenlose Mikroschleifwerkzeuge und der auftretenden elektrodynamischen Effekte

Abstract

The development of ever more compact machine tools for machining smaller pieces and their surfaces is becoming increasingly important, above all in medicine, micro-machining, optics and mechatronics. This work describes the design of a novel concept for the bearing and control of a grinding ball, which is get in rotation by a pneumatic air-driven flow. Particular emphasis is placed on the methodology and parameter studies, which in addition to analytical calculations, a 3D simulation model has been created in addition. The focus of the investigations was the systematic pre-selection of the geometry and the generation of the magnetic field in the correct sections of the calotte, the particular difficulty in the consideration of the three-dimensional force generation and in the decoupling of the magnetic and mechanical quantities.The analytical and the resulting 3D-FEM model of the magnetic bearing with respect to the tensile forces could be confirmed experimentally. The analytical results became more inaccurate as soon as the saturation in the nucleus was reached. For the field guidance in the magnetic bear a ferromagnetic material without sheets was used. Due to the electrical conductivity of the material, the propagation of the eddy currents was high pronounced. The consideration of the electrodynamic effects on the signals was absolutely necessary at high sampling rates (kHz).The investigations have shown that the method of exact linearization is most effective for the nonlinear control of the considered system. Thus, the entire working area within the form and any positions of the ball can be accurately represented. The theory of the control design is based on a nonlinear transformation in the form of tables and calculations as well as the nonlinear decoupling of currents and forces. With the new control method, a clear control structure for the magnetic bearing could be realized. The model and parameter uncertainties could be compensated by the integrator components.