A Method to Realize Low Velocity Movability and Eliminate Friction Induced Noise in Piezoelectric Ultrasonic Motors

Abstract

In a piezoelectric ultrasonic motor (USM) or resonance drive type piezoelectric motor (RPM), movement is generated between a vibrator (stator) and a slider (rotor). Since the microscopic vibrations on a stator are transferred to a slider through friction interaction, the movement of a slider has a nonlinear characteristic due to the nature of the friction force. This nonlinear behavior causes large position errors due to the occurrence of discontinuous stick-slip movements and unpleasant audible noise, especially at a low velocity drive. This friction induced acoustic sound is magnified at low velocities as the natural frequency of the mechanical system of a piezoelectric motor with mass and the holding and prestress spring forces are dependent on the closed loop motion controller. This study addresses the abovementioned issues. First, a mechanical model, which considers the nature of movements in a resonance drive type piezoelectric motor, was established. The model could suitably define the friction induced forced vibration and noise source. Second, a new driving method for resonance drive type piezoelectric motors was proposed, in which the piezoelectric vibrator was excited using two driving sources at two different frequencies. The difference between the two excitation frequencies was synchronized to the servo sampling frequency of the digital control unit. Finally, the performance of the proposed driving method was compared with those of the conventional driving methods. It was noted that in addition to the realization of silent and smooth low velocity movements, the positioning error for the linear movements between the desired and actual positions decreased to less than 10 nm for velocities ranging from 1 mm/s to 0.001 mm/s.

Data-Driven Tuning of PID Controlled Piezoelectric Ultrasonic Motor

“…Another interesting feature here is that the servo control frequency is synchronized to the frequency difference of the two driving signals. More information on dual source dual frequency driving method can also be found in previous studies [18][19][20]. The DSDF driving method allows for a silent and smooth motion at low velocities, decreasing the positioning error of linear movement to less than 10 nm for velocities from 1.0 mm/s to 0.001 mm/s.…”

“…As these issues must be dealt with while trying to obtain slow motion from an ultrasonic motor, the dual source dual frequency driving method was introduced to enhance controllability [18].…”

“…Another interesting feature here is that the servo control frequency is synchronized to the frequency difference of the two driving signals. More information on dual source dual frequency driving method can also be found in previous studies [18][19][20].…”

Nonlinear Position Control with Augmented Observer in Brushless DC Motor

“…In [14], position, velocity, and load torque were estimated using both back-emf injection and velocity variation; however, because the estimated load torque is calculated by neglecting friction, an estimation error is inevitable. There are various approaches for the friction compensation using the friction modeling or the friction identification [15][16][17][18][19][20][21]; however, it is difficult to compensate for the friction because there are various frictions such as viscous friction, static friction, and Coulomb friction.…”

2020 Index IEEE/ASME Transactions on Mechatronics Vol. 25

“…AcousticsA Method to Realize Low Velocity Movability and Eliminate Friction Induced Noise in Piezoelectric Ultrasonic Motors Delibas, B., +, TMECH Dec. 2020. 2677-2687 Actuators A Compression Valve for Sanitary Control of Fluid-Driven Actuators.…”