A Methodology for the Optimal Design of Linear Ultrasonic Actuators

Linear ultrasonic motors (LUSMs) are a type of piezoelectric actuator that can achieve closed-loop positioning accuracy in the nanometre range. The operating principle of the LUSM is based on two stages of energy conversion. A primary challenge facing the design of LUSMs is the ability to accurately evaluate actuator-based output performance parameters in a simulated environment. This challenge limits the use of these parameters in computer-aided design optimizations. Furthermore, this issue has led to a heavy emphasis on the stator design, where the scope is limited to the mechanical design aspect of the first stage of energy conversion.;To address these issues, the overall objective of this thesis is to develop an LUSM design methodology that is capable of optimizing an LUSM configuration with respect to actuator-based performance specifications by accounting for both stages of energy conversion in its operation. By fully considering the input-output relationships in both stages of energy conversion from mechanical and electrical viewpoints, the proposed design methodology is capable of further improving the actuator output performance parameters in terms of the output force and power densities.;In this work, a novel LUSM performance evaluation and design optimization methodology is developed. The primary contribution of this methodology is its ability to evaluate both stator-based and actuator-based performance parameters in a single design stage under contact conditions found in the stator-operating environment. This approach allows the design optimization of LUSMs to be performed with respect to the actuator output performance parameters.;The performance evaluation and optimization approach enables the improvement of the LUSM output performance parameters through the application of non-sinusoidal periodic excitation voltage signals in driving the LUSM stator. Two actuation approaches were considered: the application of a square-wave excitation voltage and the application of an excitation voltage yielding a square-wave-based stator driving tip trajectory. The higher harmonics of the square wave were able to excite additional resonant modes in the stator. Performance analysis and extensive finite element-based simulations indicated significant improvements compared to sinusoidal excitation signals in terms of output force and power.