Online Controller for a Piezoelectric Motor Youssef Baba, Mostafa Bouzi, Ismail Lagrat * , Mounir Derri Univ Hassan 1 st , Laboratory of Mechanical Engineering, Industrial Management and Innovation Faculty of Science and Technology, Settat, Morocco * National School of Applied Sciences, Khouribga, Morocco Abstract— Traveling-wave ultrasonic motor has nonlinear characteristics, which varies with driving conditions associated the variations of temperature and applied load torque. In this work, a simple online speed controller is designed to improve the control performance of the motor. First, this paper suggests a Matlab-Simulink model of a traveling-wave ultrasonic motor, which defines the reference model. Then the controller based on an online tuning method is proposed to identify the plant parameters and detect the parameter variations of the motor immediately, so as to compensate it. Finally, the simulation results are described to confirm the effectiveness of the proposed method. The drive frequency is used as the input for the speed control scheme. Keywords— Ultrasonic Motor, Speed Control, Tuning Algorithm. I. INTRODUCTION The traveling-wave ultrasonic motor has excellent performance and many useful features such as high holding torque, high torque at low speed, quiet operation, simple structure, compact size, and no electromagnetic interferences. However, the dynamical characteristics of the traveling-wave ultrasonic motor are complicated and highly nonlinear, and the motor parameters are time-varying due to temperature rise and changes in motor drive operating conditions [1]. Therefore, it is difficult to predict the performance characteristics of this motor under various working conditions. The classical PID-control has more applications because the simple structure is easier for engineering design. But the fixed PID gains are hard to deal with the traveling-wave ultrasonic motor because the nonlinear and time-varying characteristics. Thus the control performance is not good. Therefore control strategies such as using adaptive PID- control, sliding mode control, fuzzy control and neural network control algorithms are put forward successively, which have obviously improved ultrasonic motor control performances [2-7]. But the complexity of these methods is great. For example, the fuzzy- neural control [7] combines the advantages of fuzzy logic and neural network, which can greatly increase control accuracy. However, it requires a large amount of calculation which increases the cost of hardware and software. This kind of control is expensive and confined only to high-precision applications. In this paper, the speed control of a traveling-wave ultrasonic motor (USR60) based on an online algorithm is designed. This control algorithm compensates the speed characteristic variations of the motor with on-line parameters identification. The proposed control scheme, therefore, has robustness in terms of parameter variations. The model reference is obtained by Matlab-simulink model simulations, and the driving frequency is adopted as the control input. The paper is organized as follows: in section 2, a mathematical model of the motor is presented and a reference model for USR60 is proposed, so as to control the motor. Section 3, introduces the proposed online controller. Simulation results are presented in section 4. Section 5 offers our concluding remarks. II. USR60 MODEL Traveling-wave ultrasonic motors are complex electromechanical devices in which a mechanical resonant vibration is exited in the stator through proper forcing piezoelectric ceramics. This stator vibration is transformed into a rotation through friction contact between the stator and rotor. The model of piezoelectric and stator can be described by the following equation M D C v F d        (1) with  represents the modal amplitude of the vibrating system (ceramics and stator), M is the total mass matrix of system(ceramics and stator), D is the structural damping matrix assumed to be diagonal, and C is the total stiffness matrix.  is the electromechanical coupling matrix and v is the voltage excitation vector. The term d F is a nonlinear modal force vector to consider the interaction between the stator/rotor-contact. In dealing with the dynamics of the rotor, two degrees of freedom must be taken into account: first the rotation of the rotor and second the motion in z-direction. The motion in z-direction is represented by the quantity w . The dynamics of the vertical rotor motion is obtained by the following equation r z z n mw dw F F    (2) with r m is the mass of the rotor, z d is the damping of the vertical motion, and n F is the applied axial force. The equation of rotational motion is calculated by r r r l J d T T      (3) where r J is the rotor inertia, r d denotes the damping in spinning direction, and l T is the applied torque. In Fig. 1 the Matlab-simulink model of USR60 is described. The curves in Fig. 2 are derived from calculations using the Matlab-simulink model. The speed versus drive frequency for different applied load torques is represented in Fig. 2. The speed of the motor has its maximum at the mechanical resonant frequency (40 kHz). It is International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 www.ijert.org IJERTV4IS110208 (This work is licensed under a Creative Commons Attribution 4.0 International License.) Vol. 4 Issue 11, November-2015 464