International Journal of Engineering &Technology IJET-IJENS Vol: 10 No: 01 70  Abstract— This paper aims to design a fuzzy controller to manipulate piezoelectric (PZT) actuators for nanopositioning applications. A Bouc-Wen model is adopted to represent the dynamics and hysteresis behavior in a piezo-actuated positioning stage. A simulation work is carried out for fuzzy control development and the results are compared to that obtained using PI controller based on observer. The results affirmed the potential of the developed fuzzy control algorithm whereas the tracking error is reduced to a sub-nanometer precision. Index Terms—Actuators, Fuzzy control, Nanotechnology, Position control. I. INTRODUCTION ecent advances in precision engineering and the concurrent development of advanced manufacturing techniques have the result that machined and manufactured components are no longer restricted to micrometer scale, but can now be fabricated at nanometer scale. The advanced technologies have given rise to an urgent requirement for the development of precise positioning systems capable of executing displacements with nano scale resolution. So, the nanopositioning has become an important developing target for meeting the requirements of the semiconductor, optical communication, biomedical applications, precise industrial applications, …etc [1]. Piezoelectric actuators are chosen to design precise positioning systems for achieving the sub-micro or nanopositioning applications such as scanning tunneling microscopy, biomedical equipments, nano robots, automotive industry, …etc [2-3]. The most commonly produced piezoelectric ceramics are lead-zirconate-titanate (PZT). Piezoelectric material is used to convert electrical energy to mechanical energy and vice-versa. Piezoelectric sensors are used in a variety of applications to convert mechanical energy to electrical energy such as: pressure-sensing applications, detecting imbalances of rotating machine parts, ultrasonic level measurement, flow rate measurement, sound transmitters (buzzers), sound receivers (microphones), …etc. However, piezoelectric actuators convert electrical energy to mechanical Manuscript received January 10, 2010. This work was supported in part by KSU – KETT- KACST, KSA research project (08-NAN388-2). Basem M. Bader is a Master student in Automatic Control, Electrical Engineering Department, College of Engineering, King Saud University, KSA (e-mail: bbadr1@ksu.edu.sa ). Wahied G. Ali is with Electrical Engineering Department, College of Engineering, King Saud University, KSA, on leave from Ain Shams University, Cairo, Egypt. (e-mail: wahied@ksu.edu.sa ). energy, and are used in many applications such as: scanning microscopy, patch clamp, gene manipulation, vibration cancellation, R/W head testing, hydraulic valves, drilling equipment, …etc. PZT actuators have many advantages such as [2]-[5]: - Piezoelectric actuators have excellent resolution in displacement, high stiffness, high electrical mechanical coupling efficiency, small size, small heat expansion, low power consumption and fast response. - The piezoelectric actuators make motion in micrometer range with sub-nanometer precision. - There are no moving parts in contact with each other to limit the resolution. - The piezoelectric actuators capable of moving loads of several tons and cover travel ranges of several (100 μm) with resolutions in the sub-nanometer range [2]. - The piezoelectric actuators behave pure capacitive load, so they consumes virtually no power. - The piezoelectric actuators do not produce magnetic field nor are they affected by them. However, the piezoelectric actuators have the disadvantage of hysteresis, resonant frequency and creep behaviors, which severely limit system performance such as giving rise to undesirable inaccuracy or oscillations, even leading to instability [6], [7]. Therefore, appropriate closed-loop control methodologies have been established to achieve the desired positioning accuracy of the piezoelectric actuation systems. Recent applications include a combination of a feed-forward model in a feedback control with an input shaper [8], a tracking control of a piezoelectric actuator with feed-forward hysteresis compensation [9]-[10], PI control with inverse model compensation [11], sliding-mode control [12], and fuzzy control methodology [13]. However, Ofri et al. used a control strategy based on fuzzy logic theory for vibration damping of a large flexible space structure controlled by bonded piezoceramic actuators [14], as fuzzy controllers are most suitable for systems that cannot be precisely described by mathematical formulations [13]. This paper is organized as follows. Section I presents the literature work and research motivations in nanopositioning control using PZT actuators. Section II describes the dynamic model for PZT actuated positioning stage. The developed control algorithms: PI based observer as developed in the literature and the proposed fuzzy controller are introduced in Section III. Simulation results are presented and discussed in Section IV. Finally, conclusion is drawn in Section V. Nanopositioning Fuzzy Control for Piezoelectric Actuators R Basem M. Badr and Wahied. G. Ali