Dynamic Coupling Force Compensation for Direct-Driven Machine Tools

This contribution is concerned with the improvement of dynamic precision for direct driven servo axes at machine tools. Due to coupling forces, the dynamic performance of direct-driven machines is still restricted. Therefore, we analyzed the effect of kinetic coupling in typical machine tool applications and derived a simplified dynamic model to predict the acceleration dependent disturbance forces. Effective disturbance force compensation requires suitable force- or torque inputs. State-of-the-art servo controllers for machine tools have no accessible interfaces and standard numerical control systems for machine tools do not support any model based control approach to compensate dynamic coupling forces. Therefore a hardware extension, based on a universal encoder interpolator, is presented that enables the load force compensation also for standard control systems. The measured position of the incremental encoder is modified to realize the additional force/torque input. This enables the machine tool manufacturer to compensate coupling forces independently from the control system manufacturer. The practical benefit of this hardware extension is illustrated for a newly developed direct driven machine tool manipulator.