Robust internal loop compensator design for motion control of precision linear motor

The authors propose a robust internal loop compensator and its optimal design method based on H∞ control. The controller consists of two parts, internal and external loops. The internal loop is used as a compensator for canceling disturbances including difference between reference model and real system, and external loop is designed to meet the performance criterion. The property of the internal loop compensator is compared with that of disturbance observer. Different from the disturbance observer, controller gains and Q filter can be systematically designed, instead of heuristically selected, in the proposed internal loop compensator structure. The proposed controller structure of internal and external loop is characterized by compensator design using reference model, insensitivity of the compensated system to modeling inaccuracies and unknown external disturbances, and satisfaction of desired performance specifications. The performance of proposed controller is demonstrated by experiments of a twin-servo mechanism using two brushless DC linear servo motors