Decentralized high precision motion control for nanopositioning and nanomeasuring machines

The presented work concerns a model-based friction compensation scheme which is able to improve the dynamical behavior of a two dimensional high precision positioning stage. The proposed structure consists of a state space controller and a disturbance observer. The system model for the state space controller represents the inertia as well as the friction force, it utilizes the elasto-plastic friction model. A Kalman filter serves as disturbance observer. The developed model-based control scheme is used for one axis of the positioning stage. For control of both axes of the fine positioning stage a decentralized approach is presented. In an extensive experimental study the proposed scheme is compared to a well tuned PID controller without friction cancellation as well as the state space controller without observer. Experiments show that the dynamical behavior of the system can be improved significantly. In all test scenarios the presented structure produces the smallest tracking error. The decentralized control approach shows, that the axes of the experimental set-up are coupled and a model-based decoupling can possibly lead to a further reduction of the tracking error.