Controller-integrated predictive oscillation compensation for machine tools with parallel kinematics

Since computerised numerical control (CNC) systems were introduced into the field of mechanical engineering, the manufacturing technology made significant progress. In spite of drastic improvements, mainly in terms of productivity and precision (e.g. finishing surface quality), opportunities for further advancements for the manufacturing processes still exist. One possible method for increasing precision is to adopt a machine structure with parallel kinematics. This kinematic structure can enhance the system dynamics, because the moving mass is divided among all actuators, contrary to the conventional, cartesian machine structures. The problem, which still exists even with this new structural solution, is the machine oscillation that appears during machining. This oscillation may decrease the machining accuracy. This paper highlights a new possible method to compensate the machine oscillation by using a controller-integrated compensation principle. Because of this principle, additional mechanical components (e.g. piezo stacks, actuators) are not necessary. This compensation concept was developed and verified under Matlab/SIMULINK and then installed into the machining centre Dyna-M. The kinematic structure of Dyna-M is defined as a hybrid-kinematic and also one of the typical parallel structures. The obtained results show up to 60% reduction of the machine oscillation and prove the practical usability of this compensation system.