14. Trajectory Tracking and Active Vibration Suppression on a Flexible Tower Crane

This work deals with a flexible structure modeled as a tower crane, with proper servomechanisms for load manipulation. This type of flexible structure deserves popularity due to well-known advantages as high payload and large workspace. The main challenges, however, are the undesirable endogenous and exogenous vibrations attributed to typical tasks as trajectory tracking, at high speed rates, and inherent structural behavior, of tower and arm, excited by internal as external forces. The overall mechanical structure is modeled by means of finite element methods, experimental modal analysis techniques and some specific criteria are used to select the most appropriate locations of sensors and actuators. In order to attenuate these undesirable vibrations, an active tendon system is implemented, on a specific part of the structure, attaching a PZT stack actuator, on a supporting cable, to regulate its tension and to improve the effective modal damping and closed-loop stability and, as a consequence, improve the quality of the trajectory tracking and also reduce, as possible, the structural vibrations. Two active vibration control schemes are employed during the synthesis of the controller, that is, Multiple Positive Position Feedback (MPPF). Finally, the overall dynamic performance is evaluated and validated by numerical and experimental results on a small-scale mechanical platform.