Experimental Study of Active Vibration Control.

Active vibration control was implemented on two laboratory structures having some important dynamic characteristics of large space structures a dynamically uncomplicated beam-cable structure and a dynamically complicated plane grid structure. The control techniques used are direct-velocity-feedback control, with a single colocated sensor-actuator pair, and modal-space control, with a single sensor and several actuators. The most challenging control task attempted was modal-space control of five low frequency modes of the plane grid structure, including a closely spaced pair. But interference between the two close modes produced a mild instability of the structure-control system. Subsequently, a stable four mode controller was produced by simply disabling the control of the mode which had driven the unstable motion. Satisfactory agreement between theoretical predictions and experimental measurements was achieved in this research. However, the nature of the inevitable differences observed suggests in general that any active vibration control technique implemented on a dynamically complicated large space structure should be insensitive to errors in the structure model used to design the control, because that model is unlikely to predict accurately the parameters of all modes affected by the control.