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

Abstract

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. I Introduction Flexible structures are increasingly being used in space robotics and other industries. These flexible structures are generally lightweight and have relatively low damping for the fundamental and initial few modes. The flexibility of the robot arms causes elastic vibration, which tends to adversely affect the performance of the end-effector. This in turn causes problems in modeling and control design. In addition, the frequency associated with these modes is low. Thus control of these modes becomes an important issue. Some functions performed on the International Space Station (ISS) require stringent requirements in terms of vibration isolation and suppression where smart materials utilization can lead to lightweight design. In the last few years the concept of intelligent material system and structures has been proposed by many research groups.[1],[2],[3]. According to the definition of smart material system active component and phases are considered as part of the structure. Such active phases can be obtained by using active