A method of designing a robust force controller of a water-hydraulic servo system

Abstract

Robust force control of a water-hydraulic servo system is discussed. The system treated in this paper is a model of a moulding press used for a fabrication process of large-scale integration packages. The whole surface of a wafer is covered with a thin plastic layer by the press. The performance of force control is important to obtain sufficient quality. The press is driven by a ram cylinder and a water-hydraulic servo valve. Considering the uncertainty caused by the flow characteristics of the valve in the overlap region and the mechanical stiffness of the press, a method of designing a robust force controller is proposed by applying H∞ control theory. Qualitative evaluation of modelling error is the key to the design of the robust controller. The performance of the robust controller is examined using an experimental water-hydraulic servo system set-up. It is illustrated how the system responses are influenced by the weighting function parameters of H∞ control theory.