Model-based control of an active fixture for advanced aerospace components

In this paper the dynamical behaviour of a flexible part and an actively controlled fixture system is studied. Four active clamps are used for the control of the part-fixture system. Advanced finite element (FE) analyses have been carried out to model the part and the adaptive clamps. An accurate small-sized model of the part is established using the Craig-Bampton reduction method. A second-order model has been established for the adaptive clamps on the basis of the FE model. The supports and part-fixture contacts are modelled as spring-dashpot elements. Piezoelectric actuators are utilized to provide the forces required for the adaptive clamping scheme. A model-based control architecture has been incorporated and proportional integral (PI) controllers are established for the individual clamps. After investigating the performance of the controllers for dynamic compensation, analysis shows that PI control can be used effectively to minimize the reaction forces on the supports, induced by deflection caused by machining forces.