HYSTERESIS AND VIBRATION COMPENSATION IN PIEZOELECTRIC ACTUATORS BY INTEGRATING CHARGE CONTROL AND INVERSE FEEDFORWARD 1 G M Clayton *,2 S Tien * A J Fleming **,3 S O R Moheimani ** S Devasia * * Department of Mechanical Engineering University of Washington Box 352600, Seattle, WA 98195, USA ** School of Electrical Engineering and Computer Science University of Newcastle University Drive, Callaghan, NSW 2308, Australia Abstract: In this paper we address the problems of hysteresis and vibrations that limit the accuracy of piezoelectric positioners. It is widely known that the use of charge control significantly reduces hysteresis, thus enabling high-accuracy positioning during low speed operations. However, charge control is unable to reduce vibrations that limit the positioning bandwidth. Our main contribution is to overcome this bandwidth limitation by augmenting charge control with inverse feedforward to compensate for vibrations, resulting in a high-bandwidth, high- accuracy positioning system. We apply this integrated method to a piezoelectric tube actuator and experimental results are presented to illustrate the positioning improvements with the proposed integrated approach. Keywords: Hysteresis, Vibration, Piezopositioners, Feedforward, Charge Control 1. INTRODUCTION In this article we address the problems of hystere- sis and induced mechanical vibrations that limit the accuracy of piezoelectric positioners (piezopo- sitioners). Piezopositioners offer sub-angstrom po- sitioning resolution over micron scale ranges and have been widely used in mechatronic systems developed for such purposes as nanofabrication (Quate, 1997) and scanning probe microscopy (SPM) (Binnig and Smith, 1986). Although the positioning resolution of piezopositioners is high, 1 This work supported by NSF Grant: CMS 0301787 2 email: gclayton@u.washington.edu 3 email: andrew.fleming@newcastle.edu.au the positioning accuracy is severely limited by hysteresis and vibrations. This loss of position- ing accuracy can lead to undesired effects such as errant surface modification in nanofabrication (Hiura, 2003) or image distortions in scanning probe microscopy (Barrett and Quate, 1991). In this article we propose an integrated approach to compensate for both effects. Recent improve- ments in charge amplifiers have enabled easy implementation of charge control (Fleming and Moheimani, 2006) (where the piezo is driven by charge as opposed to voltage), which significantly reduces hysteresis-caused positioning errors (New- comb and Flinn, 1982). However, charge con- trol cannot reduce vibration-caused positioning 812