Vibration Suppression of Flexible-Link Manipulator by PZT Actuators and Sensors

In this paper a vibration suppression control system by piezoelectric actuators and sensors is presented for a one flexible link manipulators for space activities. This research is innovative because of the very high flexibility, stringent pointing requirements and a low first vibration frequency. In the last years there has been a large number of studies on the possible use of distributed actuators and sensors, in the framework of 'smart' materials technology. Among the various available materials for smart structures actuators and sensors, lead zirconate titanate piezoceramics (PZT) patches are very attractive: they undergo mechanical stresses and strain when subjected to an applied electric field and, vice-versa, generate an electric field in response to mechanical stresses and strains. They are easy to bond to a structure, and their high stiffness makes it possible to induce high strain energy in the system. In fact it is possible to bond or even embed these materials into a passive traditional structure to perform both sensing and actuation functions, provided that appropriate placement and size is chosen for them. In this paper, a Linear Quadratic Regulator controller (LQR) for vibration suppression is used on both an aluminum link with bonded PZT patches and a carbon fiber link with embedded PZT patches. One test with aluminum link is conducted also with the link mounted on an Harmonic Drive motor. Some experimental tests of vibration suppression, to validate the proposed method, are presented. This experiment has been performed at the Spacecraft Robotics Laboratory of Naval Postgraduate School at Monterey, while the carbon fiber link were manufactured at Politecnico di Milano.