Finite element method based design and optimisation methodology for piezoelectric ultrasonic motors

Piezoelectric ultrasonic motors are superior to electromagnetic micro motors, because their efficiency remains theoretically constant during miniaturization. However, the still relatively recent technology has a considerable unexploited optimisation potential. Numerical structural analysis by the means of the finite element method (FEM) is a common approach for dimensioning piezoelectric motors. Consequently, there is a need for efficient optimisation procedures adapted to the FEM simulation. We developed a dedicated design methodology that combines sensitivity analysis and FEM based optimisation algorithms. It enables a good understanding of how the geometrical and physical parameters govern the movement of the motor. The parameters with an important impact on the objective function, the vibration amplitude of the stator, are free during optimisation, the others are fixed. Functional models of rotary and linear motors are built in order to demonstrate their operation. Interferometric vibration measurements validate quantitatively the FEM model along with the suggested design methodology.