Data-Driven Tuning of PID Controlled Piezoelectric Ultrasonic Motor

Ultrasonic motors employ resonance to amplify the vibrations of piezoelectric actuator, offering precise positioning and relatively long travel distances and making them ideal for robotic, optical, metrology and medical applications. As operating in resonance and force transfer through friction lead to nonlinear characteristics like creep and hysteresis, it is difficult to apply model-based control, so data-driven control offers a good alternative. Data-driven techniques are used here for iterative feedback tuning of a proportional integral derivative (PID) controller parameters and comparing between different motor driving techniques, single source and dual source dual frequency (DSDF). The controller and stage system used are both produced by the company Physik Instrumente GmbH, where a PID controller is tuned with the help of four search methods: grid search, Luus–Jaakola method, genetic algorithm, and a new hybrid method developed that combines elements of grid search and Luus–Jaakola method. The latter method was found to be quick to converge and produced consistent result, similar to the Luus–Jaakola method. Genetic Algorithm was much slower and produced sub optimal results. The grid search has also proven the DSDF driving method to be robust, less parameter dependent, and produces far less integral position error than the single source driving method.

Design of Unimorph Type 3DOF Ultrasonic Motor

A new design of 3 degrees of freedom (DOF) piezoelectric ultrasonic motor (USM) is introduced in this paper. The concept of this design is to incorporate a spherical rotor between two piezoelectric transducers. Each transducer is coupled with a flange, and it operates like a unimorph structure. Such a design of the transducer allows to increase the amplitude of the vibrations and to generate the higher torque and driving force used to achieve 3DOF rotary motion of the spherical rotor. The proposed USM may be used for humanoid robots, optomechanical systems, or small satellites. This USM consists of several components, is lightweight and reliable. Numerical analysis and experimental studies were performed to validate the feasibility of this drive, to find out proper resonant frequencies for the unimorph, and optimize the shape of the flange. Experimental studies were accomplished to validate the results of the numerical analysis and to validate the operating principles of the piezoelectric motor.