Model based control of machine tool manipulators

This contribution is concerned with the improvement of dynamic precision for direct-driven servo axes at machine tools. Due to coupling forces and structural vibrations, the dynamic performance of direct-driven machines is still restricted. Therefore, we analysed the effect of kinetic coupling in typical machine tool applications and derived a simplified dynamic model for predicting acceleration-dependent disturbance forces. Special consideration is given to the additional damping of elastic structural components. Their effect on the feedback-controlled system is described by a simplified but suitable dynamic model that allows state observation and effective parameter identification for all relevant cases of structural flexibility. This leads to an extension of standard servo drives by a robust state space controller. Standard numerical control systems for machine tools do not support model based control. Therefore special functions on a commercial numerical control system have been developed to compensate dynamic coupling forces and to damp dominating structural modes. The practical benefit of these special functions is illustrated for a newly developed direct-driven machine tool manipulator.