Glossiotis G., Antoniadis I.

Flexible structures are used in a wide range of engineering applications, which take advantage of their lightweight features and their inherent capability to decrease the energy consumption. However, the motion of flexible structures excites transient and residual vibrations and for this reason numerous command preconditioning techniques have been developed, with various degrees of effectiveness concerning vibration suppression. The basic aspect that these methods have to confront is the contradicting requirements between the speed of response of the system and the robustness to variations of its natural frequencies. Among those command-preconditioning methods, Finite Impulse Response (FIR) filters can present an extremely robust behavior, combined with the introduction of the minimum possible delay. This optimal combination renders FIR filters applicable in a wide range of engineering applications, where wide bands of structural resonances are excited. Such a typical flexible truss is considered, characterized by wide bands of dense clusters of eigenfrequencies. The truss considered in the paper is appropriately constructed to include a number of attributes typically present in large flexible structures, and especially their characteristics related to the excitation of lightly dumped modes. The flexible structure is attached to the end point of a hydraulic Cartesian manipulator, by the use of which the motion commands are generated. A FIR filter based preconditioning scheme is implemented for the motion control, while the dynamic behavior of the system is assisted by three accelerometers and pressure gauges for the hydraulic circuit. The corresponding experimental results demonstrate that the resulting filtered motion commands effectively suppress the excited vibrations, covering in the best possible way all the excited modes of the structure.