In this paper, we study the closed-loop subspace identification of MIMO motion system with flexible structures. The fundamental objective of identification experiment is to achieve the state space model for motion control. The model with flexible structures of the motion system is analyzed and deduced to the form of state space model, which is composed with rigid modes and flexible modes. As the stability and safety case, the closed-loop subspace identification method is employed. The proposed identification method is suitable for modern control algorithms to construct space state model. The rigid and flexible modes are obtained and updated by the modal approach. Identification experiment is carried on the industrial wafer stage, which is the typical MIMO motion system with flexible structures. The results of experiment verify the feasibility and validity of the proposed identification method.
