A Closed-Loop Micro-Ultrasonic Motor Control System With Extremum Seeking

Microactuators are an essential technology to revolutionize existing micromachines, but making them closed-loop controlled with an internal sensor is a great challenge due to the limited size of the components. In this paper, we build a micro-ultrasonic motor in the 2–3 mm scale, combine it with a tunneling magneto resistance (TMR) sensor with dimensions of 1.4 mm
$\times1$
mm, and construct a closed-loop system with a control algorithm. It is currently the smallest rotary actuator-sensor system assembled into a size with a height of 3.2 mm, a width of 3.2 mm, and a length of 5 mm. In the system, we attempt to solve a steady-state error problem for the micro-ultrasonic motor’s internal parameter changes, such as a temperature rise and the resonant frequency variation. A model-free, real-time-adaptive extremum seeking controller (ESC) that continuously tracks and localizes the optimum driving frequency is implemented into the system for the desired rotation with minimum steady-state error. Although the controller is simply designed, experiments show a good accordance between the resulting angular velocity and the reference.