Effective Control of a Six Degree of Freedom Shake Table

Abstract

Real-Time Hybrid Substructuring (RTHS) is a new method of vibration testing that can be used to effectively characterize the system level performance of mechanical equipment. RTHS allows mechanical equipment to be physically tested while coupled through what is called a transfer system to a real-time numerical simulation of the support structure. The challenge in applying RTHS to test mechanical equipment is twofold: the equipment itself can have little inherent damping which, coupled with the inherent dynamics in the transfer system, can result in unstable RTHS tests; and the interface at the attachment points can be complex with multi-directional and rotational motion and reactions which adds significant complexity to the RTHS transfer system. To insure stability and accurately represent the complex interface between the physical and numerical substructures, a high fidelity multiple-input-multiple-output (MIMO) servo-hydraulic actuator system is needed for the RTHS transfer system. This paper presents a methodology to achieve effective control of a six degree-of-freedom (6DOF) shake table and describes the corresponding MIMO system identification and model-based feedforward feedback compensation to facilitate both stable and accurate RTHS testing of lightly damped mechanical systems. Results show that the proposed compensation method can improve the magnitude and phase tracking of a 6DOF shake table located at the University of Connecticut.