Effective Force Testing Using A Robust Loop Shaping Controller

Effective force testing (EFT) is one of the force-based experimental methods used for performance evaluation of structures that incorporate dynamic force control using hydraulic actuators. While previous studies have shown successful implementations of force control, controllable frequency ranges are limited to low frequencies (10 Hz). This study presents the EFT method using a robust loop shaping force feedback controller that can extend the frequency range up to 25 Hz or even higher. Unlike the conventional PID controllers, loop shaping controllers can provide robustness for a high level of force measurement noise. This study investigates the dynamic properties of hydraulic actuators and the design of a loop shaping controller that compensates for control-structure interaction as well as suppresses the effect of oil-column resonance. The designed loop shaping controller was successfully implemented into an EFT setup at the Johns Hopkins University. An experimental investigation of the loop shaping controller was performed under step, random and earthquake force loadings. Experimental results showed that the loop shaping controller provided excellent force tracking performance as well as robustness for dynamic force loadings. It was also shown that the loop shaping controller had the gain margin of 9.54 dB at the frequency of 28 Hz.